diff options
| author | Paul E. McKenney <paulmck@kernel.org> | 2022-09-26 08:57:56 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2022-10-21 10:08:43 -0700 |
| commit | e9f8a790bf682bb4a2f79d0d905b34d55bceb71d (patch) | |
| tree | 98bc145b5a7058418583d51108c55d08b109eca2 /include/linux/slab.h | |
| parent | aba9645bd10bd9f793732b06495b1312ee44865e (diff) | |
slab: Explain why SLAB_TYPESAFE_BY_RCU reference before locking
It is not obvious to the casual user why it is absolutely necessary to
acquire a reference to a SLAB_TYPESAFE_BY_RCU structure before acquiring
a lock in that structure. Therefore, add a comment explaining this point.
[ paulmck: Apply Vlastimil Babka feedback. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: <linux-mm@kvack.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Diffstat (limited to 'include/linux/slab.h')
| -rw-r--r-- | include/linux/slab.h | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/include/linux/slab.h b/include/linux/slab.h index 90877fcde70b..487418c7ea8c 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -76,6 +76,17 @@ * rcu_read_lock before reading the address, then rcu_read_unlock after * taking the spinlock within the structure expected at that address. * + * Note that it is not possible to acquire a lock within a structure + * allocated with SLAB_TYPESAFE_BY_RCU without first acquiring a reference + * as described above. The reason is that SLAB_TYPESAFE_BY_RCU pages + * are not zeroed before being given to the slab, which means that any + * locks must be initialized after each and every kmem_struct_alloc(). + * Alternatively, make the ctor passed to kmem_cache_create() initialize + * the locks at page-allocation time, as is done in __i915_request_ctor(), + * sighand_ctor(), and anon_vma_ctor(). Such a ctor permits readers + * to safely acquire those ctor-initialized locks under rcu_read_lock() + * protection. + * * Note that SLAB_TYPESAFE_BY_RCU was originally named SLAB_DESTROY_BY_RCU. */ /* Defer freeing slabs to RCU */ |