mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-11 02:26:45 +07:00
4cc7b9544b
Originally we used a mutex to protect concurrent devmap update
and delete operations from racing with netdev unregister notifier
callbacks.
The notifier hook is needed because we increment the netdev ref
count when a dev is added to the devmap. This ensures the netdev
reference is valid in the datapath. However, we don't want to block
unregister events, hence the initial mutex and notifier handler.
The concern was in the notifier hook we search the map for dev
entries that hold a refcnt on the net device being torn down. But,
in order to do this we require two steps,
(i) dereference the netdev: dev = rcu_dereference(map[i])
(ii) test ifindex: dev->ifindex == removing_ifindex
and then finally we can swap in the NULL dev in the map via an
xchg operation,
xchg(map[i], NULL)
The danger here is a concurrent update could run a different
xchg op concurrently leading us to replace the new dev with a
NULL dev incorrectly.
CPU 1 CPU 2
notifier hook bpf devmap update
dev = rcu_dereference(map[i])
dev = rcu_dereference(map[i])
xchg(map[i]), new_dev);
rcu_call(dev,...)
xchg(map[i], NULL)
The above flow would create the incorrect state with the dev
reference in the update path being lost. To resolve this the
original code used a mutex around the above block. However,
updates, deletes, and lookups occur inside rcu critical sections
so we can't use a mutex in this context safely.
Fortunately, by writing slightly better code we can avoid the
mutex altogether. If CPU 1 in the above example uses a cmpxchg
and _only_ replaces the dev reference in the map when it is in
fact the expected dev the race is removed completely. The two
cases being illustrated here, first the race condition,
CPU 1 CPU 2
notifier hook bpf devmap update
dev = rcu_dereference(map[i])
dev = rcu_dereference(map[i])
xchg(map[i]), new_dev);
rcu_call(dev,...)
odev = cmpxchg(map[i], dev, NULL)
Now we can test the cmpxchg return value, detect odev != dev and
abort. Or in the good case,
CPU 1 CPU 2
notifier hook bpf devmap update
dev = rcu_dereference(map[i])
odev = cmpxchg(map[i], dev, NULL)
[...]
Now 'odev == dev' and we can do proper cleanup.
And viola the original race we tried to solve with a mutex is
corrected and the trace noted by Sasha below is resolved due
to removal of the mutex.
Note: When walking the devmap and removing dev references as needed
we depend on the core to fail any calls to dev_get_by_index() using
the ifindex of the device being removed. This way we do not race with
the user while searching the devmap.
Additionally, the mutex was also protecting list add/del/read on
the list of maps in-use. This patch converts this to an RCU list
and spinlock implementation. This protects the list from concurrent
alloc/free operations. The notifier hook walks this list so it uses
RCU read semantics.
BUG: sleeping function called from invalid context at kernel/locking/mutex.c:747
in_atomic(): 1, irqs_disabled(): 0, pid: 16315, name: syz-executor1
1 lock held by syz-executor1/16315:
#0: (rcu_read_lock){......}, at: [<ffffffff8c363bc2>] map_delete_elem kernel/bpf/syscall.c:577 [inline]
#0: (rcu_read_lock){......}, at: [<ffffffff8c363bc2>] SYSC_bpf kernel/bpf/syscall.c:1427 [inline]
#0: (rcu_read_lock){......}, at: [<ffffffff8c363bc2>] SyS_bpf+0x1d32/0x4ba0 kernel/bpf/syscall.c:1388
Fixes: 2ddf71e23c
("net: add notifier hooks for devmap bpf map")
Reported-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
435 lines
13 KiB
C
435 lines
13 KiB
C
/* Copyright (c) 2017 Covalent IO, Inc. http://covalent.io
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of version 2 of the GNU General Public
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* License as published by the Free Software Foundation.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*/
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/* Devmaps primary use is as a backend map for XDP BPF helper call
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* bpf_redirect_map(). Because XDP is mostly concerned with performance we
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* spent some effort to ensure the datapath with redirect maps does not use
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* any locking. This is a quick note on the details.
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*
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* We have three possible paths to get into the devmap control plane bpf
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* syscalls, bpf programs, and driver side xmit/flush operations. A bpf syscall
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* will invoke an update, delete, or lookup operation. To ensure updates and
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* deletes appear atomic from the datapath side xchg() is used to modify the
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* netdev_map array. Then because the datapath does a lookup into the netdev_map
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* array (read-only) from an RCU critical section we use call_rcu() to wait for
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* an rcu grace period before free'ing the old data structures. This ensures the
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* datapath always has a valid copy. However, the datapath does a "flush"
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* operation that pushes any pending packets in the driver outside the RCU
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* critical section. Each bpf_dtab_netdev tracks these pending operations using
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* an atomic per-cpu bitmap. The bpf_dtab_netdev object will not be destroyed
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* until all bits are cleared indicating outstanding flush operations have
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* completed.
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*
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* BPF syscalls may race with BPF program calls on any of the update, delete
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* or lookup operations. As noted above the xchg() operation also keep the
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* netdev_map consistent in this case. From the devmap side BPF programs
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* calling into these operations are the same as multiple user space threads
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* making system calls.
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*
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* Finally, any of the above may race with a netdev_unregister notifier. The
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* unregister notifier must search for net devices in the map structure that
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* contain a reference to the net device and remove them. This is a two step
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* process (a) dereference the bpf_dtab_netdev object in netdev_map and (b)
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* check to see if the ifindex is the same as the net_device being removed.
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* When removing the dev a cmpxchg() is used to ensure the correct dev is
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* removed, in the case of a concurrent update or delete operation it is
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* possible that the initially referenced dev is no longer in the map. As the
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* notifier hook walks the map we know that new dev references can not be
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* added by the user because core infrastructure ensures dev_get_by_index()
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* calls will fail at this point.
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*/
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#include <linux/bpf.h>
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#include <linux/jhash.h>
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#include <linux/filter.h>
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#include <linux/rculist_nulls.h>
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#include "percpu_freelist.h"
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#include "bpf_lru_list.h"
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#include "map_in_map.h"
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struct bpf_dtab_netdev {
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struct net_device *dev;
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int key;
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struct rcu_head rcu;
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struct bpf_dtab *dtab;
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};
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struct bpf_dtab {
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struct bpf_map map;
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struct bpf_dtab_netdev **netdev_map;
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unsigned long int __percpu *flush_needed;
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struct list_head list;
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};
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static DEFINE_SPINLOCK(dev_map_lock);
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static LIST_HEAD(dev_map_list);
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static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
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{
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struct bpf_dtab *dtab;
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u64 cost;
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int err;
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/* check sanity of attributes */
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if (attr->max_entries == 0 || attr->key_size != 4 ||
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attr->value_size != 4 || attr->map_flags)
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return ERR_PTR(-EINVAL);
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/* if value_size is bigger, the user space won't be able to
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* access the elements.
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*/
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if (attr->value_size > KMALLOC_MAX_SIZE)
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return ERR_PTR(-E2BIG);
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dtab = kzalloc(sizeof(*dtab), GFP_USER);
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if (!dtab)
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return ERR_PTR(-ENOMEM);
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/* mandatory map attributes */
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dtab->map.map_type = attr->map_type;
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dtab->map.key_size = attr->key_size;
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dtab->map.value_size = attr->value_size;
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dtab->map.max_entries = attr->max_entries;
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dtab->map.map_flags = attr->map_flags;
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err = -ENOMEM;
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/* make sure page count doesn't overflow */
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cost = (u64) dtab->map.max_entries * sizeof(struct bpf_dtab_netdev *);
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cost += BITS_TO_LONGS(attr->max_entries) * sizeof(unsigned long);
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if (cost >= U32_MAX - PAGE_SIZE)
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goto free_dtab;
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dtab->map.pages = round_up(cost, PAGE_SIZE) >> PAGE_SHIFT;
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/* if map size is larger than memlock limit, reject it early */
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err = bpf_map_precharge_memlock(dtab->map.pages);
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if (err)
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goto free_dtab;
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err = -ENOMEM;
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/* A per cpu bitfield with a bit per possible net device */
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dtab->flush_needed = __alloc_percpu(
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BITS_TO_LONGS(attr->max_entries) *
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sizeof(unsigned long),
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__alignof__(unsigned long));
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if (!dtab->flush_needed)
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goto free_dtab;
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dtab->netdev_map = bpf_map_area_alloc(dtab->map.max_entries *
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sizeof(struct bpf_dtab_netdev *));
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if (!dtab->netdev_map)
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goto free_dtab;
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spin_lock(&dev_map_lock);
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list_add_tail_rcu(&dtab->list, &dev_map_list);
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spin_unlock(&dev_map_lock);
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return &dtab->map;
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free_dtab:
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free_percpu(dtab->flush_needed);
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kfree(dtab);
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return ERR_PTR(err);
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}
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static void dev_map_free(struct bpf_map *map)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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int i, cpu;
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/* At this point bpf_prog->aux->refcnt == 0 and this map->refcnt == 0,
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* so the programs (can be more than one that used this map) were
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* disconnected from events. Wait for outstanding critical sections in
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* these programs to complete. The rcu critical section only guarantees
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* no further reads against netdev_map. It does __not__ ensure pending
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* flush operations (if any) are complete.
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*/
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synchronize_rcu();
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/* To ensure all pending flush operations have completed wait for flush
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* bitmap to indicate all flush_needed bits to be zero on _all_ cpus.
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* Because the above synchronize_rcu() ensures the map is disconnected
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* from the program we can assume no new bits will be set.
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*/
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for_each_online_cpu(cpu) {
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unsigned long *bitmap = per_cpu_ptr(dtab->flush_needed, cpu);
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while (!bitmap_empty(bitmap, dtab->map.max_entries))
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cpu_relax();
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}
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/* Although we should no longer have datapath or bpf syscall operations
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* at this point we we can still race with netdev notifier, hence the
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* lock.
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*/
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for (i = 0; i < dtab->map.max_entries; i++) {
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struct bpf_dtab_netdev *dev;
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dev = dtab->netdev_map[i];
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if (!dev)
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continue;
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dev_put(dev->dev);
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kfree(dev);
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}
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/* At this point bpf program is detached and all pending operations
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* _must_ be complete
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*/
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spin_lock(&dev_map_lock);
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list_del_rcu(&dtab->list);
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spin_unlock(&dev_map_lock);
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free_percpu(dtab->flush_needed);
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bpf_map_area_free(dtab->netdev_map);
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kfree(dtab);
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}
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static int dev_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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u32 index = key ? *(u32 *)key : U32_MAX;
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u32 *next = (u32 *)next_key;
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if (index >= dtab->map.max_entries) {
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*next = 0;
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return 0;
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}
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if (index == dtab->map.max_entries - 1)
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return -ENOENT;
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*next = index + 1;
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return 0;
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}
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void __dev_map_insert_ctx(struct bpf_map *map, u32 key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
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__set_bit(key, bitmap);
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}
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struct net_device *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct bpf_dtab_netdev *dev;
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if (key >= map->max_entries)
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return NULL;
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dev = READ_ONCE(dtab->netdev_map[key]);
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return dev ? dev->dev : NULL;
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}
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/* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled
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* from the driver before returning from its napi->poll() routine. The poll()
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* routine is called either from busy_poll context or net_rx_action signaled
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* from NET_RX_SOFTIRQ. Either way the poll routine must complete before the
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* net device can be torn down. On devmap tear down we ensure the ctx bitmap
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* is zeroed before completing to ensure all flush operations have completed.
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*/
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void __dev_map_flush(struct bpf_map *map)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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unsigned long *bitmap = this_cpu_ptr(dtab->flush_needed);
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u32 bit;
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for_each_set_bit(bit, bitmap, map->max_entries) {
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struct bpf_dtab_netdev *dev = READ_ONCE(dtab->netdev_map[bit]);
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struct net_device *netdev;
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/* This is possible if the dev entry is removed by user space
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* between xdp redirect and flush op.
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*/
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if (unlikely(!dev))
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continue;
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netdev = dev->dev;
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__clear_bit(bit, bitmap);
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if (unlikely(!netdev || !netdev->netdev_ops->ndo_xdp_flush))
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continue;
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netdev->netdev_ops->ndo_xdp_flush(netdev);
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}
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}
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/* rcu_read_lock (from syscall and BPF contexts) ensures that if a delete and/or
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* update happens in parallel here a dev_put wont happen until after reading the
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* ifindex.
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*/
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static void *dev_map_lookup_elem(struct bpf_map *map, void *key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct bpf_dtab_netdev *dev;
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u32 i = *(u32 *)key;
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if (i >= map->max_entries)
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return NULL;
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dev = READ_ONCE(dtab->netdev_map[i]);
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return dev ? &dev->dev->ifindex : NULL;
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}
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static void dev_map_flush_old(struct bpf_dtab_netdev *old_dev)
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{
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if (old_dev->dev->netdev_ops->ndo_xdp_flush) {
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struct net_device *fl = old_dev->dev;
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unsigned long *bitmap;
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int cpu;
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for_each_online_cpu(cpu) {
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bitmap = per_cpu_ptr(old_dev->dtab->flush_needed, cpu);
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__clear_bit(old_dev->key, bitmap);
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fl->netdev_ops->ndo_xdp_flush(old_dev->dev);
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}
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}
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}
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static void __dev_map_entry_free(struct rcu_head *rcu)
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{
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struct bpf_dtab_netdev *old_dev;
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old_dev = container_of(rcu, struct bpf_dtab_netdev, rcu);
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dev_map_flush_old(old_dev);
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dev_put(old_dev->dev);
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kfree(old_dev);
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}
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static int dev_map_delete_elem(struct bpf_map *map, void *key)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct bpf_dtab_netdev *old_dev;
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int k = *(u32 *)key;
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if (k >= map->max_entries)
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return -EINVAL;
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/* Use synchronize_rcu() here to ensure any rcu critical sections
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* have completed, but this does not guarantee a flush has happened
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* yet. Because driver side rcu_read_lock/unlock only protects the
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* running XDP program. However, for pending flush operations the
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* dev and ctx are stored in another per cpu map. And additionally,
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* the driver tear down ensures all soft irqs are complete before
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* removing the net device in the case of dev_put equals zero.
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*/
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old_dev = xchg(&dtab->netdev_map[k], NULL);
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if (old_dev)
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call_rcu(&old_dev->rcu, __dev_map_entry_free);
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return 0;
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}
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static int dev_map_update_elem(struct bpf_map *map, void *key, void *value,
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u64 map_flags)
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{
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struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
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struct net *net = current->nsproxy->net_ns;
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struct bpf_dtab_netdev *dev, *old_dev;
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u32 i = *(u32 *)key;
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u32 ifindex = *(u32 *)value;
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if (unlikely(map_flags > BPF_EXIST))
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return -EINVAL;
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if (unlikely(i >= dtab->map.max_entries))
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return -E2BIG;
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if (unlikely(map_flags == BPF_NOEXIST))
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return -EEXIST;
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if (!ifindex) {
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dev = NULL;
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} else {
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dev = kmalloc(sizeof(*dev), GFP_ATOMIC | __GFP_NOWARN);
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if (!dev)
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return -ENOMEM;
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dev->dev = dev_get_by_index(net, ifindex);
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if (!dev->dev) {
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kfree(dev);
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return -EINVAL;
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}
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dev->key = i;
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dev->dtab = dtab;
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}
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/* Use call_rcu() here to ensure rcu critical sections have completed
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* Remembering the driver side flush operation will happen before the
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* net device is removed.
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*/
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old_dev = xchg(&dtab->netdev_map[i], dev);
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if (old_dev)
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call_rcu(&old_dev->rcu, __dev_map_entry_free);
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return 0;
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}
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const struct bpf_map_ops dev_map_ops = {
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.map_alloc = dev_map_alloc,
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.map_free = dev_map_free,
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.map_get_next_key = dev_map_get_next_key,
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.map_lookup_elem = dev_map_lookup_elem,
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.map_update_elem = dev_map_update_elem,
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.map_delete_elem = dev_map_delete_elem,
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};
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static int dev_map_notification(struct notifier_block *notifier,
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ulong event, void *ptr)
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{
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struct net_device *netdev = netdev_notifier_info_to_dev(ptr);
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struct bpf_dtab *dtab;
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int i;
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switch (event) {
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case NETDEV_UNREGISTER:
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/* This rcu_read_lock/unlock pair is needed because
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* dev_map_list is an RCU list AND to ensure a delete
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* operation does not free a netdev_map entry while we
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* are comparing it against the netdev being unregistered.
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*/
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rcu_read_lock();
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list_for_each_entry_rcu(dtab, &dev_map_list, list) {
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for (i = 0; i < dtab->map.max_entries; i++) {
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struct bpf_dtab_netdev *dev, *odev;
|
|
|
|
dev = READ_ONCE(dtab->netdev_map[i]);
|
|
if (!dev ||
|
|
dev->dev->ifindex != netdev->ifindex)
|
|
continue;
|
|
odev = cmpxchg(&dtab->netdev_map[i], dev, NULL);
|
|
if (dev == odev)
|
|
call_rcu(&dev->rcu,
|
|
__dev_map_entry_free);
|
|
}
|
|
}
|
|
rcu_read_unlock();
|
|
break;
|
|
default:
|
|
break;
|
|
}
|
|
return NOTIFY_OK;
|
|
}
|
|
|
|
static struct notifier_block dev_map_notifier = {
|
|
.notifier_call = dev_map_notification,
|
|
};
|
|
|
|
static int __init dev_map_init(void)
|
|
{
|
|
register_netdevice_notifier(&dev_map_notifier);
|
|
return 0;
|
|
}
|
|
|
|
subsys_initcall(dev_map_init);
|