| Message ID | 20180620224147.23777-1-shakeelb@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, 20 Jun 2018, Shakeel Butt wrote: > For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs > allocated per node for a kmem_cache. Thus, slabs_node() in > __kmem_cache_empty(), __kmem_cache_shrink() and __kmem_cache_destroy() > will always return 0 for such config. This is wrong and can cause issues > for all users of these functions. CONFIG_SLUB_DEBUG is set by default on almost all builds. The only case where CONFIG_SLUB_DEBUG is switched off is when we absolutely need to use the minimum amount of memory (embedded or some such thing). > The right solution is to make slabs_node() work even for > !CONFIG_SLUB_DEBUG. The commit 0f389ec63077 ("slub: No need for per node > slab counters if !SLUB_DEBUG") had put the per node slab counter under > CONFIG_SLUB_DEBUG because it was only read through sysfs API and the > sysfs API was disabled on !CONFIG_SLUB_DEBUG. However the users of the > per node slab counter assumed that it will work in the absence of > CONFIG_SLUB_DEBUG. So, make the counter work for !CONFIG_SLUB_DEBUG. Please do not do this. Find a way to avoid these checks. The objective of a !CONFIG_SLUB_DEBUG configuration is to not compile in debuggin checks etc etc in order to reduce the code/data footprint to the minimum necessary while sacrificing debuggability etc etc. Maybe make it impossible to disable CONFIG_SLUB_DEBUG if CGROUPs are in use?
On Wed, Jun 20, 2018 at 6:15 PM Christopher Lameter <cl@linux.com> wrote: > > On Wed, 20 Jun 2018, Shakeel Butt wrote: > > > For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs > > allocated per node for a kmem_cache. Thus, slabs_node() in > > __kmem_cache_empty(), __kmem_cache_shrink() and __kmem_cache_destroy() > > will always return 0 for such config. This is wrong and can cause issues > > for all users of these functions. > > > CONFIG_SLUB_DEBUG is set by default on almost all builds. The only case > where CONFIG_SLUB_DEBUG is switched off is when we absolutely need to use > the minimum amount of memory (embedded or some such thing). > > > The right solution is to make slabs_node() work even for > > !CONFIG_SLUB_DEBUG. The commit 0f389ec63077 ("slub: No need for per node > > slab counters if !SLUB_DEBUG") had put the per node slab counter under > > CONFIG_SLUB_DEBUG because it was only read through sysfs API and the > > sysfs API was disabled on !CONFIG_SLUB_DEBUG. However the users of the > > per node slab counter assumed that it will work in the absence of > > CONFIG_SLUB_DEBUG. So, make the counter work for !CONFIG_SLUB_DEBUG. > > Please do not do this. Find a way to avoid these checks. The > objective of a !CONFIG_SLUB_DEBUG configuration is to not compile in > debuggin checks etc etc in order to reduce the code/data footprint to the > minimum necessary while sacrificing debuggability etc etc. > > Maybe make it impossible to disable CONFIG_SLUB_DEBUG if CGROUPs are in > use? > Copying from the other thread: On Wed, Jun 20, 2018 at 6:22 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > On Thu, Jun 21, 2018 at 3:20 AM Christopher Lameter <cl@linux.com> wrote: > > > > NAK. Its easier to simply not allow !CONFIG_SLUB_DEBUG for cgroups based > > configs because in that case you certainly have enough memory to include > > the runtime debug code as well as the extended counters. > > > > FWIW, I ran into issues with a combination of KASAN+CONFIG_SLUB > without having CONFIG_SLUB_DEBUG, because KASAN was using functions > that were broken without CONFIG_SLUB_DEBUG, so while you're at it with > creating dependencies, you might want to also say KASAN+CONFIG_SLUB > ==> CONFIG_SLUB_DEBUG. KASAN is the only user of __kmem_cache_empty(). So, enforcing KASAN+CONFIG_SLUB => CONFIG_SLUB_DEBUG makes sense but not sure about cgroups or memcg. Though is it ok let __kmem_cache_shrink() & __kmem_cache_shutdown() be broken for !CONFIG_SLUB_DEBUG? For __kmem_cache_shutdown(), I can understand that shutting down a kmem_cache when there are still objects allocated from it, is broken and wrong. For __kmem_cache_shrink(), maybe wrong answer from it is tolerable. Shakeel
On Thu 21-06-18 01:15:30, Cristopher Lameter wrote: > On Wed, 20 Jun 2018, Shakeel Butt wrote: > > > For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs > > allocated per node for a kmem_cache. Thus, slabs_node() in > > __kmem_cache_empty(), __kmem_cache_shrink() and __kmem_cache_destroy() > > will always return 0 for such config. This is wrong and can cause issues > > for all users of these functions. > > > CONFIG_SLUB_DEBUG is set by default on almost all builds. The only case > where CONFIG_SLUB_DEBUG is switched off is when we absolutely need to use > the minimum amount of memory (embedded or some such thing). I thought those would be using SLOB rather than SLUB. > > > The right solution is to make slabs_node() work even for > > !CONFIG_SLUB_DEBUG. The commit 0f389ec63077 ("slub: No need for per node > > slab counters if !SLUB_DEBUG") had put the per node slab counter under > > CONFIG_SLUB_DEBUG because it was only read through sysfs API and the > > sysfs API was disabled on !CONFIG_SLUB_DEBUG. However the users of the > > per node slab counter assumed that it will work in the absence of > > CONFIG_SLUB_DEBUG. So, make the counter work for !CONFIG_SLUB_DEBUG. > > Please do not do this. Find a way to avoid these checks. The > objective of a !CONFIG_SLUB_DEBUG configuration is to not compile in > debuggin checks etc etc in order to reduce the code/data footprint to the > minimum necessary while sacrificing debuggability etc etc. > > Maybe make it impossible to disable CONFIG_SLUB_DEBUG if CGROUPs are in > use? Why don't we simply remove the config option altogether and make it enabled effectively.
On Thu, Jun 21, 2018 at 8:01 AM Michal Hocko <mhocko@kernel.org> wrote: > > On Thu 21-06-18 01:15:30, Cristopher Lameter wrote: > > On Wed, 20 Jun 2018, Shakeel Butt wrote: > > > > > For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs > > > allocated per node for a kmem_cache. Thus, slabs_node() in > > > __kmem_cache_empty(), __kmem_cache_shrink() and __kmem_cache_destroy() > > > will always return 0 for such config. This is wrong and can cause issues > > > for all users of these functions. > > > > > > CONFIG_SLUB_DEBUG is set by default on almost all builds. The only case > > where CONFIG_SLUB_DEBUG is switched off is when we absolutely need to use > > the minimum amount of memory (embedded or some such thing). > > I thought those would be using SLOB rather than SLUB. > > > > > > The right solution is to make slabs_node() work even for > > > !CONFIG_SLUB_DEBUG. The commit 0f389ec63077 ("slub: No need for per node > > > slab counters if !SLUB_DEBUG") had put the per node slab counter under > > > CONFIG_SLUB_DEBUG because it was only read through sysfs API and the > > > sysfs API was disabled on !CONFIG_SLUB_DEBUG. However the users of the > > > per node slab counter assumed that it will work in the absence of > > > CONFIG_SLUB_DEBUG. So, make the counter work for !CONFIG_SLUB_DEBUG. > > > > Please do not do this. Find a way to avoid these checks. The > > objective of a !CONFIG_SLUB_DEBUG configuration is to not compile in > > debuggin checks etc etc in order to reduce the code/data footprint to the > > minimum necessary while sacrificing debuggability etc etc. > > > > Maybe make it impossible to disable CONFIG_SLUB_DEBUG if CGROUPs are in > > use? > > Why don't we simply remove the config option altogether and make it > enabled effectively. > Christopher, how do you want to proceed? I don't have any strong opinion. I just don't want KASAN users kept broken for SLUB. thanks, Shakeel
diff --git a/mm/slab.h b/mm/slab.h index 68bdf498da3b..a6545332cc86 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -473,8 +473,8 @@ struct kmem_cache_node { #ifdef CONFIG_SLUB unsigned long nr_partial; struct list_head partial; -#ifdef CONFIG_SLUB_DEBUG atomic_long_t nr_slabs; +#ifdef CONFIG_SLUB_DEBUG atomic_long_t total_objects; struct list_head full; #endif diff --git a/mm/slub.c b/mm/slub.c index a3b8467c14af..c9c190d54687 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -1030,42 +1030,6 @@ static void remove_full(struct kmem_cache *s, struct kmem_cache_node *n, struct list_del(&page->lru); } -/* Tracking of the number of slabs for debugging purposes */ -static inline unsigned long slabs_node(struct kmem_cache *s, int node) -{ - struct kmem_cache_node *n = get_node(s, node); - - return atomic_long_read(&n->nr_slabs); -} - -static inline unsigned long node_nr_slabs(struct kmem_cache_node *n) -{ - return atomic_long_read(&n->nr_slabs); -} - -static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects) -{ - struct kmem_cache_node *n = get_node(s, node); - - /* - * May be called early in order to allocate a slab for the - * kmem_cache_node structure. Solve the chicken-egg - * dilemma by deferring the increment of the count during - * bootstrap (see early_kmem_cache_node_alloc). - */ - if (likely(n)) { - atomic_long_inc(&n->nr_slabs); - atomic_long_add(objects, &n->total_objects); - } -} -static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects) -{ - struct kmem_cache_node *n = get_node(s, node); - - atomic_long_dec(&n->nr_slabs); - atomic_long_sub(objects, &n->total_objects); -} - /* Object debug checks for alloc/free paths */ static void setup_object_debug(struct kmem_cache *s, struct page *page, void *object) @@ -1321,16 +1285,46 @@ slab_flags_t kmem_cache_flags(unsigned int object_size, #define disable_higher_order_debug 0 +#endif /* CONFIG_SLUB_DEBUG */ + static inline unsigned long slabs_node(struct kmem_cache *s, int node) - { return 0; } +{ + struct kmem_cache_node *n = get_node(s, node); + + return atomic_long_read(&n->nr_slabs); +} + static inline unsigned long node_nr_slabs(struct kmem_cache_node *n) - { return 0; } -static inline void inc_slabs_node(struct kmem_cache *s, int node, - int objects) {} -static inline void dec_slabs_node(struct kmem_cache *s, int node, - int objects) {} +{ + return atomic_long_read(&n->nr_slabs); +} -#endif /* CONFIG_SLUB_DEBUG */ +static inline void inc_slabs_node(struct kmem_cache *s, int node, int objects) +{ + struct kmem_cache_node *n = get_node(s, node); + + /* + * May be called early in order to allocate a slab for the + * kmem_cache_node structure. Solve the chicken-egg + * dilemma by deferring the increment of the count during + * bootstrap (see early_kmem_cache_node_alloc). + */ + if (likely(n)) { + atomic_long_inc(&n->nr_slabs); +#ifdef CONFIG_SLUB_DEBUG + atomic_long_add(objects, &n->total_objects); +#endif + } +} +static inline void dec_slabs_node(struct kmem_cache *s, int node, int objects) +{ + struct kmem_cache_node *n = get_node(s, node); + + atomic_long_dec(&n->nr_slabs); +#ifdef CONFIG_SLUB_DEBUG + atomic_long_sub(objects, &n->total_objects); +#endif +} /* * Hooks for other subsystems that check memory allocations. In a typical
For !CONFIG_SLUB_DEBUG, SLUB does not maintain the number of slabs allocated per node for a kmem_cache. Thus, slabs_node() in __kmem_cache_empty(), __kmem_cache_shrink() and __kmem_cache_destroy() will always return 0 for such config. This is wrong and can cause issues for all users of these functions. Infact in [1] Jason has reported a system crash while using SLUB without CONFIG_SLUB_DEBUG. The reason was the usage of slabs_node() by __kmem_cache_empty(). The right solution is to make slabs_node() work even for !CONFIG_SLUB_DEBUG. The commit 0f389ec63077 ("slub: No need for per node slab counters if !SLUB_DEBUG") had put the per node slab counter under CONFIG_SLUB_DEBUG because it was only read through sysfs API and the sysfs API was disabled on !CONFIG_SLUB_DEBUG. However the users of the per node slab counter assumed that it will work in the absence of CONFIG_SLUB_DEBUG. So, make the counter work for !CONFIG_SLUB_DEBUG. Please note that commit f9e13c0a5a33 ("slab, slub: skip unnecessary kasan_cache_shutdown()") exposed this issue but it is present even before. [1] http://lkml.kernel.org/r/CAHmME9rtoPwxUSnktxzKso14iuVCWT7BE_-_8PAC=pGw1iJnQg@mail.gmail.com Fixes: f9e13c0a5a33 ("slab, slub: skip unnecessary kasan_cache_shutdown()") Signed-off-by: Shakeel Butt <shakeelb@google.com> Suggested-by: David Rientjes <rientjes@google.com> Reported-by: Jason A . Donenfeld <Jason@zx2c4.com> Cc: Christoph Lameter <cl@linux.com> Cc: Pekka Enberg <penberg@kernel.org> Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: <stable@vger.kernel.org> Cc: <linux-mm@kvack.org> Cc: <linux-kernel@vger.kernel.org> --- mm/slab.h | 2 +- mm/slub.c | 80 +++++++++++++++++++++++++------------------------------ 2 files changed, 38 insertions(+), 44 deletions(-)