Lockless __ptr_ring_empty requires that consumer head is read and
written at once, atomically. Annotate accordingly to make sure compiler
does it correctly. Switch locked callers to __ptr_ring_peek which does
not support the lockless operation.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
The only function safe to call without locks
is __ptr_ring_empty. Move documentation about
lockless use there to make sure people do not
try to use __ptr_ring_peek outside locks.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
The comment near __ptr_ring_peek says:
* If ring is never resized, and if the pointer is merely
* tested, there's no need to take the lock - see e.g. __ptr_ring_empty.
but this was in fact never possible since consumer_head would sometimes
point outside the ring. Refactor the code so that it's always
pointing within a ring.
Fixes: c5ad119fb6 ("net: sched: pfifo_fast use skb_array")
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This explains why is the net usage of __ptr_ring_peek
actually ok without locks.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
When running consumer and/or producer operations and empty checks in
parallel its possible to have the empty check run past the end of the
array. The scenario occurs when an empty check is run while
__ptr_ring_discard_one() is in progress. Specifically after the
consumer_head is incremented but before (consumer_head >= ring_size)
check is made and the consumer head is zeroe'd.
To resolve this, without having to rework how consumer/producer ops
work on the array, simply add an extra dummy slot to the end of the
array. Even if we did a rework to avoid the extra slot it looks
like the normal case checks would suffer some so best to just
allocate an extra pointer.
Reported-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Fixes: c5ad119fb6 ("net: sched: pfifo_fast use skb_array")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Users of ptr_ring expect that it's safe to give the
data structure a pointer and have it be available
to consumers, but that actually requires an smb_wmb
or a stronger barrier.
In absence of such barriers and on architectures that reorder writes,
consumer might read an un=initialized value from an skb pointer stored
in the skb array. This was observed causing crashes.
To fix, add memory barriers. The barrier we use is a wmb, the
assumption being that producers do not need to read the value so we do
not need to order these reads.
Reported-by: George Cherian <george.cherian@cavium.com>
Suggested-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
As found by syzkaller, malicious users can set whatever tx_queue_len
on a tun device and eventually crash the kernel.
Lets remove the ALIGN(XXX, SMP_CACHE_BYTES) thing since a small
ring buffer is not fast anyway.
Fixes: 2e0ab8ca83 ("ptr_ring: array based FIFO for pointers")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch introduce a batched version of consuming, consumer can
dequeue more than one pointers from the ring at a time. We don't care
about the reorder of reading here so no need for compiler barrier.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Applications that consume a batch of entries in one go
can benefit from ability to return some of them back
into the ring.
Add an API for that - assuming there's space. If there's no space
naturally can't do this and have to drop entries, but this implies ring
is full so we'd likely drop some anyway.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
A known weakness in ptr_ring design is that it does not handle well the
situation when ring is almost full: as entries are consumed they are
immediately used again by the producer, so consumer and producer are
writing to a shared cache line.
To fix this, add batching to consume calls: as entries are
consumed do not write NULL into the ring until we get
a multiple (in current implementation 2x) of cache lines
away from the producer. At that point, write them all out.
We do the write out in the reverse order to keep
producer from sharing cache with consumer for as long
as possible.
Writeout also triggers when ring wraps around - there's
no special reason to do this but it helps keep the code
a bit simpler.
What should we do if getting away from producer by 2 cache lines
would mean we are keeping the ring moe than half empty?
Maybe we should reduce the batching in this case,
current patch simply reduces the batching.
Notes:
- it is no longer true that a call to consume guarantees
that the following call to produce will succeed.
No users seem to assume that.
- batching can also in theory reduce the signalling rate:
users that would previously send interrups to the producer
to wake it up after consuming each entry would now only
need to do this once in a batch.
Doing this would be easy by returning a flag to the caller.
No users seem to do signalling on consume yet so this was not
implemented yet.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Resizing currently drops consumer lock. This can cause entries to be
reordered, which isn't good in itself. More importantly, consumer can
detect a false ring empty condition and block forever.
Further, nesting of consumer within producer lock is problematic for
tun, since it produces entries in a BH, which causes a lock order
reversal:
CPU0 CPU1
---- ----
consume:
lock(&(&r->consumer_lock)->rlock);
resize:
local_irq_disable();
lock(&(&r->producer_lock)->rlock);
lock(&(&r->consumer_lock)->rlock);
<Interrupt>
produce:
lock(&(&r->producer_lock)->rlock);
To fix, nest producer lock within consumer lock during resize,
and keep consumer lock during the whole swap operation.
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Cc: stable@vger.kernel.org
Cc: "David S. Miller" <davem@davemloft.net>
Acked-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Sometimes, we need support resizing multiple queues at once. This is
because it was not easy to recover to recover from a partial failure
of multiple queues resizing.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Sometimes, we need zero length ring. But current code will crash since
we don't do any check before accessing the ring. This patch fixes this.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This adds ring resize support. Seems to be necessary as
users such as tun allow userspace control over queue size.
If resize is used, this costs us ability to peek at queue without
consumer lock - should not be a big deal as peek and consumer are
usually run on the same CPU.
If ring is made bigger, ring contents is preserved. If ring is made
smaller, extra pointers are passed to an optional destructor callback.
Cleanup function also gains destructor callback such that
all pointers in queue can be cleaned up.
This changes some APIs but we don't have any users yet,
so it won't break bisect.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
A simple array based FIFO of pointers. Intended for net stack which
commonly has a single consumer/producer.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
