Messages in this thread | | | Date | Wed, 13 Jul 2022 20:10:12 +0800 | Subject | Re: [PATCH v2 1/3] mm/slub: fix the race between validate_slab and slab_free | From | Rongwei Wang <> |
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On 7/13/22 6:22 PM, Hyeonggon Yoo wrote: > On Tue, Jul 12, 2022 at 10:28:05AM +0800, Rongwei Wang wrote: >> In use cases where allocating and freeing slab frequently, some >> error messages, such as "Left Redzone overwritten", "First byte >> 0xbb instead of 0xcc" would be printed when validating slabs. >> That's because an object has been filled with SLAB_RED_INACTIVE, >> but has not been added to slab's freelist. And between these >> two states, the behaviour of validating slab is likely to occur. >> >> Actually, it doesn't mean the slab can not work stably. But, these >> confusing messages will disturb slab debugging more or less. >> >> Signed-off-by: Rongwei Wang <rongwei.wang@linux.alibaba.com> >> --- >> mm/slub.c | 43 +++++++++++++++++++++++++------------------ >> 1 file changed, 25 insertions(+), 18 deletions(-) >> > > This makes the code more complex. > > A part of me says it may be more pleasant to split implementation > allocating from caches for debugging. That would make it simpler. > > something like: > > __slab_alloc() { > if (kmem_cache_debug(s)) > slab_alloc_debug() > else > ___slab_alloc() > } > > slab_free() { > if (kmem_cache_debug(s)) > slab_free_debug() > else > __do_slab_free() > } Oh, I also have same idea, but not sure whether it is accepted because of it needs more changes than now. Since you agree with this way, I can rewrite this code.
Thanks. > > See also: > https://lore.kernel.org/lkml/faf416b9-f46c-8534-7fb7-557c046a564d@suse.cz/ Thanks, it seems that I had missed it. > >> diff --git a/mm/slub.c b/mm/slub.c >> index b1281b8654bd..e950d8df8380 100644 >> --- a/mm/slub.c >> +++ b/mm/slub.c >> @@ -1391,18 +1391,16 @@ static noinline int free_debug_processing( >> void *head, void *tail, int bulk_cnt, >> unsigned long addr) >> { >> - struct kmem_cache_node *n = get_node(s, slab_nid(slab)); >> void *object = head; >> int cnt = 0; >> - unsigned long flags, flags2; >> + unsigned long flags; >> int ret = 0; >> depot_stack_handle_t handle = 0; >> >> if (s->flags & SLAB_STORE_USER) >> handle = set_track_prepare(); >> >> - spin_lock_irqsave(&n->list_lock, flags); >> - slab_lock(slab, &flags2); >> + slab_lock(slab, &flags); >> >> if (s->flags & SLAB_CONSISTENCY_CHECKS) { >> if (!check_slab(s, slab)) >> @@ -1435,8 +1433,7 @@ static noinline int free_debug_processing( >> slab_err(s, slab, "Bulk freelist count(%d) invalid(%d)\n", >> bulk_cnt, cnt); >> >> - slab_unlock(slab, &flags2); >> - spin_unlock_irqrestore(&n->list_lock, flags); >> + slab_unlock(slab, &flags); >> if (!ret) >> slab_fix(s, "Object at 0x%p not freed", object); >> return ret; >> @@ -3330,7 +3327,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, >> >> { >> void *prior; >> - int was_frozen; >> + int was_frozen, to_take_off = 0; >> struct slab new; >> unsigned long counters; >> struct kmem_cache_node *n = NULL; >> @@ -3341,14 +3338,23 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, >> if (kfence_free(head)) >> return; >> >> - if (kmem_cache_debug(s) && >> - !free_debug_processing(s, slab, head, tail, cnt, addr)) >> - return; >> + n = get_node(s, slab_nid(slab)); >> + if (kmem_cache_debug(s)) { >> + int ret; >> >> - do { >> - if (unlikely(n)) { >> + spin_lock_irqsave(&n->list_lock, flags); >> + ret = free_debug_processing(s, slab, head, tail, cnt, addr); >> + if (!ret) { >> spin_unlock_irqrestore(&n->list_lock, flags); >> - n = NULL; >> + return; >> + } >> + } >> + >> + do { >> + if (unlikely(to_take_off)) { >> + if (!kmem_cache_debug(s)) >> + spin_unlock_irqrestore(&n->list_lock, flags); >> + to_take_off = 0; >> } >> prior = slab->freelist; >> counters = slab->counters; >> @@ -3369,8 +3375,6 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, >> new.frozen = 1; >> >> } else { /* Needs to be taken off a list */ >> - >> - n = get_node(s, slab_nid(slab)); >> /* >> * Speculatively acquire the list_lock. >> * If the cmpxchg does not succeed then we may >> @@ -3379,8 +3383,10 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, >> * Otherwise the list_lock will synchronize with >> * other processors updating the list of slabs. >> */ >> - spin_lock_irqsave(&n->list_lock, flags); >> + if (!kmem_cache_debug(s)) >> + spin_lock_irqsave(&n->list_lock, flags); >> >> + to_take_off = 1; >> } >> } >> >> @@ -3389,8 +3395,9 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab, >> head, new.counters, >> "__slab_free")); >> >> - if (likely(!n)) { >> - >> + if (likely(!to_take_off)) { >> + if (kmem_cache_debug(s)) >> + spin_unlock_irqrestore(&n->list_lock, flags); >> if (likely(was_frozen)) { >> /* >> * The list lock was not taken therefore no list >> -- >> 2.27.0 >>
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