lwn.git/include/linux/rhashtable.h, branch docs-next

rhashtable: consolidate hash computation in rht_key_get_hash()

2026-03-07T05:12:20+00:00

The else-if and else branches in rht_key_get_hash() both compute a hash using either params.hashfn or jhash, differing only in the source of key_len (params.key_len vs ht->p.key_len). Merge the two branches into one by using the ternary `params.key_len ?: ht->p.key_len` to select the key length, removing the duplicated logic. This also improves the performance of the else branch which previously always used jhash and never fell through to jhash2. This branch is going to be used by BPF resizable hashmap, which wraps rhashtable: https://lore.kernel.org/bpf/20260205-rhash-v1-0-30dd6d63c462@meta.com/ Signed-off-by: Mykyta Yatsenko Signed-off-by: Herbert Xu

rhashtable: Enable context analysis

2026-01-05T15:43:35+00:00

Enable context analysis for rhashtable, which was used as an initial test as it contains a combination of RCU, mutex, and bit_spinlock usage. Users of rhashtable now also benefit from annotations on the API, which will now warn if the RCU read lock is not held where required. Signed-off-by: Marco Elver Signed-off-by: Peter Zijlstra (Intel) Link: https://patch.msgid.link/20251219154418.3592607-33-elver@google.com

rhashtable: use likely for rhashtable lookup

2025-10-20T04:10:28+00:00

Sometimes, the result of the rhashtable_lookup() is expected to be found. Therefore, we can use likely() for such cases. Following new functions are introduced, which will use likely or unlikely during the lookup: rhashtable_lookup_likely rhltable_lookup_likely A micro-benchmark is made for these new functions: lookup a existed entry repeatedly for 100000000 times, and rhashtable_lookup_likely() gets ~30% speedup. Signed-off-by: Menglong Dong Signed-off-by: Herbert Xu

rhashtable: Use rcu_dereference_all and rcu_dereference_all_check

2025-09-20T12:21:03+00:00

Add rcu_dereference_all and rcu_dereference_all_check so that library code such as rhashtable can be used with any RCU variant. As it stands rcu_dereference is used within rashtable, which creates false-positive warnings if the user calls it from another RCU context, such as preempt_disable(). Use the rcu_dereference_all and rcu_dereference_all_check calls in rhashtable to suppress these warnings. Also replace the rcu_dereference_raw calls in the list iterators with rcu_dereference_all to uncover buggy calls. Reported-by: Menglong Dong Signed-off-by: Herbert Xu Reviewed-by: Paul E. McKenney Signed-off-by: Herbert Xu

rhashtable: Use __always_inline instead of inline

2025-09-06T07:57:23+00:00

Sometimes, the compiler is not clever enough to inline the rhashtable_lookup() for us, even if the "obj_cmpfn" and "key_len" in params is const. This can introduce more overhead. Therefore, use __always_inline for the rhashtable. Signed-off-by: Menglong Dong Signed-off-by: Herbert Xu

rhashtable: remove needless return in three void APIs

2025-03-17T06:24:15+00:00

Remove needless 'return' in the following void APIs: rhltable_walk_enter() rhltable_free_and_destroy() rhltable_destroy() Since both the API and callee involved are void functions. Link: https://lkml.kernel.org/r/20250221-rmv_return-v1-16-cc8dff275827@quicinc.com Signed-off-by: Zijun Hu Signed-off-by: Andrew Morton

rhashtable: Improve grammar

2024-04-03T01:03:32+00:00

Change "a" to "an" according to the usual rules, fix an "if" that was mistyped as "in", improve grammar in "considerable slow" -> "considerably slower". Signed-off-by: Jonathan Neuschäfer Reviewed-by: Randy Dunlap Link: https://lore.kernel.org/r/20240329-misc-rhashtable-v1-1-5862383ff798@gmx.net Signed-off-by: Jakub Kicinski

rhashtable: Allow rhashtable to be used from irq-safe contexts

2022-12-09T10:42:56+00:00

rhashtable currently only does bh-safe synchronization making it impossible to use from irq-safe contexts. Switch it to use irq-safe synchronization to remove the restriction. v2: Update the lock functions to return the ulong flags value and unlock functions to take the value directly instead of passing around the pointer. Suggested by Linus. Signed-off-by: Tejun Heo Reviewed-by: David Vernet Acked-by: Josh Don Acked-by: Hao Luo Acked-by: Barret Rhoden Cc: Linus Torvalds Signed-off-by: David S. Miller

rhashtable: Restore RCU marking on rhash_lock_head

2020-07-29T00:09:49+00:00

This patch restores the RCU marking on bucket_table->buckets as it really does need RCU protection. Its removal had led to a fatal bug. Signed-off-by: Herbert Xu Signed-off-by: David S. Miller

rhashtable: Fix unprotected RCU dereference in __rht_ptr

2020-07-29T00:09:49+00:00

The rcu_dereference call in rht_ptr_rcu is completely bogus because we've already dereferenced the value in __rht_ptr and operated on it. This causes potential double readings which could be fatal. The RCU dereference must occur prior to the comparison in __rht_ptr. This patch changes the order of RCU dereference so that it is done first and the result is then fed to __rht_ptr. The RCU marking changes have been minimised using casts which will be removed in a follow-up patch. Fixes: ba6306e3f648 ("rhashtable: Remove RCU marking from...") Reported-by: "Gong, Sishuai" Signed-off-by: Herbert Xu Signed-off-by: David S. Miller