We currently have no limit on the number of elements in a hash table.
This is a problem because some users (tipc) set a ceiling on the
maximum table size and when that is reached the hash table may
degenerate. Others may encounter OOM when growing and if we allow
insertions when that happens the hash table perofrmance may also
suffer.
This patch adds a new paramater insecure_max_entries which becomes
the cap on the table. If unset it defaults to max_size * 2. If
it is also zero it means that there is no cap on the number of
elements in the table. However, the table will grow whenever the
utilisation hits 100% and if that growth fails, you will get ENOMEM
on insertion.
As allowing oversubscription is potentially dangerous, the name
contains the word insecure.
Note that the cap is not a hard limit. This is done for performance
reasons as enforcing a hard limit will result in use of atomic ops
that are heavier than the ones we currently use.
The reasoning is that we're only guarding against a gross over-
subscription of the table, rather than a small breach of the limit.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
The conversion of mac80211's station table to rhashtable had a bug
that I found by accident in code review, that hadn't been found as
rhashtable apparently managed to have a maximum hash chain length
of one (!) in all our testing.
In order to test the bug and verify the fix I set my rhashtable's
max_size very low (4) in order to force getting hash collisions.
At that point, rhashtable WARNed in rhashtable_insert_rehash() but
didn't actually reject the hash table insertion. This caused it to
lose insertions - my master list of stations would have 9 entries,
but the rhashtable only had 5. This may warrant a deeper look, but
that WARN_ON() just shouldn't happen.
Fix this by not returning true from rht_grow_above_100() when the
rhashtable's max_size has been reached - in this case the user is
explicitly configuring it to be at most that big, so even if it's
now above 100% it shouldn't attempt to resize.
This fixes the "lost insertion" issue and consequently allows my
code to display its error (and verify my fix for it.)
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
nftables sets will be converted to use so called setextensions, moving
the key to a non-fixed position. To hash it, the obj_hashfn must be used,
however it so far doesn't receive the length parameter.
Pass the key length to obj_hashfn() and convert existing users.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
rhashtable_destroy() variant which stops rehashes, iterates over
the table and calls a callback to release resources.
Avoids need for nft_hash to embed rhashtable internals and allows to
get rid of the being_destroyed flag. It also saves a 2nd mutex
lock upon destruction.
Also fixes an RCU lockdep splash on nft set destruction due to
calling rht_for_each_entry_safe() without holding bucket locks.
Open code this loop as we need know that no mutations may occur in
parallel.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Introduce a new bool automatic_shrinking to require the
user to explicitly opt-in to automatic shrinking of tables.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
rhashtable_insert_rehash() requires RCU locks to be held in order
to access ht->tbl and traverse to the last table.
Fixes: ccd57b1bd3 ("rhashtable: Add immediate rehash during insertion")
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
The commit 963ecbd41a ("rhashtable:
Fix use-after-free in rhashtable_walk_stop") fixed a real bug
but created another one because we may end up sleeping inside an
RCU critical section.
This patch fixes it properly by replacing the mutex with a spin
lock that specifically protects the walker lists.
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch reintroduces immediate rehash during insertion. If
we find during insertion that the table is full or the chain
length exceeds a set limit (currently 16 but may be disabled
with insecure_elasticity) then we will force an immediate rehash.
The rehash will contain an expansion if the table utilisation
exceeds 75%.
If this rehash fails then the insertion will fail. Otherwise the
insertion will be reattempted in the new hash table.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch adds the missing bits to allow multiple rehashes. The
read-side as well as remove already handle this correctly. So it's
only the rehasher and insertion that need modification to handle
this.
Note that this patch doesn't actually enable it so for now rehashing
is still only performed by the worker thread.
This patch also disables the explicit expand/shrink interface because
the table is meant to expand and shrink automatically, and continuing
to export these interfaces unnecessarily complicates the life of the
rehasher since the rehash process is now composed of two parts.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Since every current rhashtable user uses jhash as their hash
function, the fact that jhash is an inline function causes each
user to generate a copy of its code.
This function provides a solution to this problem by allowing
hashfn to be unset. In which case rhashtable will automatically
set it to jhash. Furthermore, if the key length is a multiple
of 4, we will switch over to jhash2.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
When rht_key_hashfn is called from rhashtable itself and params
is equal to ht->p, there is no point in checking params.key_len
and falling back to ht->p.key_len.
For some reason gcc couldn't figure out that params is the same
as ht->p. So let's help it by only checking params.key_len when
it's a constant.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
We need to include linux/errno.h in rhashtable.h since it doesn't
always get included otherwise.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Now that all rhashtable users have been converted over to the
inline interface, this patch removes the unused out-of-line
interface.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch deals with the complaint that we make indirect function
calls on the fast paths unnecessarily in rhashtable. We resolve
it by moving the fast paths into inline functions that take struct
rhashtable_param (which obviously must be the same set of parameters
supplied to rhashtable_init) as an argument.
The only remaining indirect call is to obj_hashfn (or key_hashfn it
obj_hashfn is unset) on the rehash as well as the insert-during-
rehash slow path.
This patch also extends the support of vairable-length keys to
include those where the key is fixed but scattered in the object.
For example, in netlink we want to key off the namespace and the
portid but they're not next to each other.
This patch does this by directly using the object hash function
as the indicator of whether the key is accessible or not. It
also adds a new function obj_cmpfn to compare a key against an
object. This means that the caller no longer needs to supply
explicit compare functions.
All this is done in a backwards compatible manner so no existing
users are affected until they convert to the new interface.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch marks the rhashtable_init params argument const as
there is no reason to modify it since we will always make a copy
of it in the rhashtable.
This patch also fixes a bug where we don't actually round up the
value of min_size unless it is less than HASH_MIN_SIZE.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Now that nobody uses max_shift and min_shift, we can safely remove
them.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch adds the parameters max_size and min_size which are
meant to replace max_shift and min_shift.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Keeping both size and shift is silly. We only need one.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch moves future_tbl to open up the possibility of having
multiple rehashes on the same table.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch adds a rehash counter to bucket_table to indicate
the last bucket that has been rehashed. This serves two purposes:
1. Any bucket that has been rehashed can never gain a new object.
2. If the rehash counter reaches the size of the table, the table
will forever remain empty.
This patch also downsizes bucket_table->size to an unsigned int
since we do not support sizes greater than 32 bits yet.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
There is in fact no need to wait for an RCU grace period in the
rehash function, since all insertions are guaranteed to go into
the new table through spin locks.
This patch uses call_rcu to free the old/rehashed table at our
leisure.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Previously whenever the walker encountered a resize it simply
snaps back to the beginning and starts again. However, this only
works if the rehash started and completed while the walker was
idle.
If the walker attempts to restart while the rehash is still ongoing,
we may miss objects that we shouldn't have.
This patch fixes this by making the walker walk the old table
followed by the new table just like all other readers. If a
rehash is detected we will still signal our caller of the fact
so they can prepare for duplicates but we will simply continue
the walk onto the new table after the old one is finished either
by us or by the rehasher.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Commit c0c09bfdc4 ("rhashtable: avoid unnecessary wakeup for worker
queue") changed ht->shift to be atomic, which is actually unnecessary.
Instead of leaving the current shift in the core rhashtable structure,
it can be cached inside the individual bucket tables.
There, it will only be initialized once during a new table allocation
in the shrink/expansion slow path, and from then onward it stays immutable
for the rest of the bucket table liftime.
That allows shift to be non-atomic. The patch also moves hash_rnd
management into the table setup. The rhashtable structure now consumes
3 instead of 4 cachelines.
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Ying Xue <ying.xue@windriver.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Currently hash_rnd is a parameter that users can set. However,
no existing users set this parameter. It is also something that
people are unlikely to want to set directly since it's just a
random number.
In preparation for allowing the reseeding/rehashing of rhashtable,
this patch moves hash_rnd into bucket_table so that it's now an
internal state rather than a parameter.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Currently, all real users of rhashtable default their grow and shrink
decision functions to rht_grow_above_75() and rht_shrink_below_30(),
so that there's currently no need to have this explicitly selectable.
It can/should be generic and private inside rhashtable until a real
use case pops up. Since we can make this private, we'll save us this
additional indirection layer and can improve insertion/deletion time
as well.
Reference: http://patchwork.ozlabs.org/patch/443040/
Suggested-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
struct bucket_table contains mostly read fields :
size, locks_mask, locks.
Make sure these are not sharing a cache line with buckets[]
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Some existing rhashtable users get too intimate with it by walking
the buckets directly. This prevents us from easily changing the
internals of rhashtable.
This patch adds the helpers rhashtable_walk_init/exit/start/next/stop
which will replace these custom walkers.
They are meant to be usable for both procfs seq_file walks as well
as walking by a netlink dump. The iterator structure should fit
inside a netlink dump cb structure, with at least one element to
spare.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
"next" is not updated, causing an endless loop for buckets with more than
one element.
Fixes: 88d6ed15ac ("rhashtable: Convert bucket iterators to take table and index")
Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
When we put our declared work task in the global workqueue with
schedule_delayed_work(), its delay parameter is always zero.
Therefore, we should define a regular work in rhashtable structure
instead of a delayed work.
By the way, we add a condition to check whether resizing functions
are NULL before cancelling the work, avoiding to cancel an
uninitialized work.
Lastly, while we wait for all work items we submitted before to run
to completion with cancel_delayed_work(), ht->mutex has been taken in
rhashtable_destroy(). Moreover, cancel_delayed_work() doesn't return
until all work items are accomplished, and when work items are
scheduled, the work's function - rht_deferred_worker() will be called.
However, as rht_deferred_worker() also needs to acquire the lock,
deadlock might happen at the moment as the lock is already held before.
So if the cancel work function is moved out of the lock covered scope,
this will avoid the deadlock.
Fixes: 97defe1 ("rhashtable: Per bucket locks & deferred expansion/shrinking")
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
As commit c0c09bfdc4 ("rhashtable: avoid unnecessary wakeup for
worker queue") moves condition statements of verifying whether hash
table size exceeds its maximum threshold or reaches its minimum
threshold from resizing functions to resizing decision functions,
we should add a note in rhashtable.h to indicate the implementation
of what the grow and shrink decision function must enforce min/max
shift, otherwise, it's failed to take min/max shift's set watermarks
into effect.
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Introduce a new function called rhashtable_lookup_compare_insert()
which is very similar to rhashtable_lookup_insert(). But the former
makes use of users' given compare function to look for an object,
and then inserts it into hash table if found. As the entire process
of search and insertion is under protection of per bucket lock, this
can help users to avoid the involvement of extra lock.
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Move condition statements of verifying whether hash table size exceeds
its maximum threshold or reaches its minimum threshold from resizing
functions to resizing decision functions, avoiding unnecessary wakeup
for worker queue thread.
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Cc: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Involve a new function called rhashtable_lookup_insert() which makes
lookup and insertion atomic under bucket lock protection, helping us
avoid to introduce an extra lock when we search and insert an object
into hash table.
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Fixup below build error:
include/linux/rhashtable.h: At top level:
include/linux/rhashtable.h:118:34: error: field ‘mutex’ has incomplete type
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
In order to allow for wider usage of rhashtable, use a special nulls
marker to terminate each chain. The reason for not using the existing
nulls_list is that the prev pointer usage would not be valid as entries
can be linked in two different buckets at the same time.
The 4 nulls base bits can be set through the rhashtable_params structure
like this:
struct rhashtable_params params = {
[...]
.nulls_base = (1U << RHT_BASE_SHIFT),
};
This reduces the hash length from 32 bits to 27 bits.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Introduces an array of spinlocks to protect bucket mutations. The number
of spinlocks per CPU is configurable and selected based on the hash of
the bucket. This allows for parallel insertions and removals of entries
which do not share a lock.
The patch also defers expansion and shrinking to a worker queue which
allows insertion and removal from atomic context. Insertions and
deletions may occur in parallel to it and are only held up briefly
while the particular bucket is linked or unzipped.
Mutations of the bucket table pointer is protected by a new mutex, read
access is RCU protected.
In the event of an expansion or shrinking, the new bucket table allocated
is exposed as a so called future table as soon as the resize process
starts. Lookups, deletions, and insertions will briefly use both tables.
The future table becomes the main table after an RCU grace period and
initial linking of the old to the new table was performed. Optimization
of the chains to make use of the new number of buckets follows only the
new table is in use.
The side effect of this is that during that RCU grace period, a bucket
traversal using any rht_for_each() variant on the main table will not see
any insertions performed during the RCU grace period which would at that
point land in the future table. The lookup will see them as it searches
both tables if needed.
Having multiple insertions and removals occur in parallel requires nelems
to become an atomic counter.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
The removal function of nft_hash currently stores a reference to the
previous element during lookup which is used to optimize removal later
on. This was possible because a lock is held throughout calling
rhashtable_lookup() and rhashtable_remove().
With the introdution of deferred table resizing in parallel to lookups
and insertions, the nftables lock will no longer synchronize all
table mutations and the stored pprev may become invalid.
Removing this optimization makes removal slightly more expensive on
average but allows taking the resize cost out of the insert and
remove path.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Cc: netfilter-devel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
This patch is in preparation to introduce per bucket spinlocks. It
extends all iterator macros to take the bucket table and bucket
index. It also introduces a new rht_dereference_bucket() to
handle protected accesses to buckets.
It introduces a barrier() to the RCU iterators to the prevent
the compiler from caching the first element.
The lockdep verifier is introduced as stub which always succeeds
and properly implement in the next patch when the locks are
introduced.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Hash the key inside of rhashtable_lookup_compare() like
rhashtable_lookup() does. This allows to simplify the hashing
functions and keep them private.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Cc: netfilter-devel@vger.kernel.org
Signed-off-by: David S. Miller <davem@davemloft.net>
Reallocation is only required for shrinking and expanding and both rely
on a mutex for synchronization and callers of rhashtable_init() are in
non atomic context. Therefore, no reason to continue passing allocation
hints through the API.
Instead, use GFP_KERNEL and add __GFP_NOWARN | __GFP_NORETRY to allow
for silent fall back to vzalloc() without the OOM killer jumping in as
pointed out by Eric Dumazet and Eric W. Biederman.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Currently mutex_is_held can only test locks in the that are global
since it takes no arguments. This prevents rhashtable from being
used in places where locks are lock, e.g., per-namespace locks.
This patch adds a parent field to mutex_is_held and rhashtable_params
so that local locks can be used (and tested).
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
The rhashtable function mutex_is_held is only used when PROVE_LOCKING
is enabled. This patch makes the mutex_is_held field in rhashtable
optional depending on PROVE_LOCKING.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Although rhashtable library allows user to specify a quiet big size
for user's created hash table, the table may be shrunk to a
very small size - HASH_MIN_SIZE(4) after object is removed from
the table at the first time. Subsequently, even if the total amount
of objects saved in the table is quite lower than user's initial
setting in a long time, the hash table size is still dynamically
adjusted by rhashtable_shrink() or rhashtable_expand() each time
object is inserted or removed from the table. However, as
synchronize_rcu() has to be called when table is shrunk or
expanded by the two functions, we should permit user to set the
minimum table size through configuring the minimum number of shifts
according to user specific requirement, avoiding these expensive
actions of shrinking or expanding because of calling synchronize_rcu().
Signed-off-by: Ying Xue <ying.xue@windriver.com>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Call rcu_deference_raw() directly from within rht_for_each_entry_rcu()
as list_for_each_entry_rcu() does.
Fixes the following sparse warnings:
net/netlink/af_netlink.c:2906:25: expected struct rhash_head const *__mptr
net/netlink/af_netlink.c:2906:25: got struct rhash_head [noderef] <asn:4>*<noident>
Fixes: e341694e3e ("netlink: Convert netlink_lookup() to use RCU protected hash table")
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
No need to export rht_obj(), all inner to outer object translations
occur internally. It was intended to be used with rht_for_each() which
now primarily serves as the iterator for rhashtable_remove_pprev() to
effectively flush and free the full table.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Properly annotate next pointers as access is RCU protected in
the lookup path.
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Generic implementation of a resizable, scalable, concurrent hash table
based on [0]. The implementation supports both, fixed size keys specified
via an offset and length, or arbitrary keys via own hash and compare
functions.
Lookups are lockless and protected as RCU read side critical sections.
Automatic growing/shrinking based on user configurable watermarks is
available while allowing concurrent lookups to take place.
Objects to be hashed must include a struct rhash_head. The reason for not
using the existing struct hlist_head is that the expansion and shrinking
will have two buckets point to a single entry which would lead in obscure
reverse chaining behaviour.
Code includes a boot selftest if CONFIG_TEST_RHASHTABLE is defined.
[0] https://www.usenix.org/legacy/event/atc11/tech/final_files/Triplett.pdf
Signed-off-by: Thomas Graf <tgraf@suug.ch>
Reviewed-by: Nikolay Aleksandrov <nikolay@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
