On 3/15/21 6:16 PM, David Rientjes wrote:
> On Mon, 15 Mar 2021, Vlastimil Babka wrote:
>
>> Commit ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()")
>> introduced a static key to optimize the case where no debugging is enabled for
>> any cache. The static key is enabled when slub_debug boot parameter is passed,
>> or CONFIG_SLUB_DEBUG_ON enabled.
>>
>> However, some caches might be created with one or more debugging flags
>> explicitly passed to kmem_cache_create(), and the commit missed this. Thus the
>> debugging functionality would not be actually performed for these caches unless
>> the static key gets enabled by boot param or config.
>>
>> This patch fixes it by checking for debugging flags passed to
>> kmem_cache_create() and enabling the static key accordingly.
>>
>> Note such explicit debugging flags should not be used outside of debugging and
>> testing as they will now enable the static key globally. btrfs_init_cachep()
>> creates a cache with SLAB_RED_ZONE but that's a mistake that's being corrected
>> [1]. rcu_torture_stats() creates a cache with SLAB_STORE_USER, but that is a
>> testing module so it's OK and will start working as intended after this patch.
>>
>> Also note that in case of backports to kernels before v5.12 that don't have
>> 59450bbc12be ("mm, slab, slub: stop taking cpu hotplug lock"),
>> static_branch_enable_cpuslocked() should be used.
>>
>
> Since this affects 5.9+, is the plan to propose backports to stable with
> static_branch_enable_cpuslocked() once this is merged? (I notice the
> absence of the stable tag here, which I believe is intended.)
I was thinking about it, and since the rcutorture user is only in -next (AFAICS)
and btrfs user was unintended, it didn't seem to meet stable criteria to me. But
I won't mind if it's backported.
>> [1] https://lore.kernel.org/linux-btrfs/20210315141824.26099-1-dsterba@xxxxxxxx/
>>
>> Reported-by: Oliver Glitta <glittao@xxxxxxxxx>
>> Fixes: ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()")
>> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Thanks!
>> ---
>> mm/slub.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>>
>> diff --git a/mm/slub.c b/mm/slub.c
>> index 350a37f30e60..cd6694ad1a0a 100644
>> --- a/mm/slub.c
>> +++ b/mm/slub.c
>> @@ -3827,6 +3827,15 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
>>
>> static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
>> {
>> +#ifdef CONFIG_SLUB_DEBUG
>> + /*
>> + * If no slub_debug was enabled globally, the static key is not yet
>> + * enabled by setup_slub_debug(). Enable it if the cache is being
>> + * created with any of the debugging flags passed explicitly.
>> + */
>> + if (flags & SLAB_DEBUG_FLAGS)
>> + static_branch_enable(&slub_debug_enabled);
>> +#endif
>> s->flags = kmem_cache_flags(s->size, flags, s->name);
>> #ifdef CONFIG_SLAB_FREELIST_HARDENED
>> s->random = get_random_long();
>
