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    SubjectRe: [PATCH 5.10 518/530] mm, slub: enable slub_debug static key when creating cache with explicit debug flags
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    On 5/12/21 4:50 PM, Greg Kroah-Hartman wrote:
    > From: Vlastimil Babka <vbabka@suse.cz>
    >
    > [ Upstream commit 1f0723a4c0df36cbdffc6fac82cd3c5d57e06d66 ]
    >
    > 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.
    >
    > [1] https://lore.kernel.org/linux-btrfs/20210315141824.26099-1-dsterba@suse.com/
    >
    > Link: https://lkml.kernel.org/r/20210315153415.24404-1-vbabka@suse.cz
    > Fixes: ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()")
    > Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
    > Reported-by: Oliver Glitta <glittao@gmail.com>
    > Acked-by: David Rientjes <rientjes@google.com>
    > Cc: Christoph Lameter <cl@linux.com>
    > Cc: Pekka Enberg <penberg@kernel.org>
    > Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    > Cc: "Paul E. McKenney" <paulmck@kernel.org>
    > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    > Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    > Signed-off-by: Sasha Levin <sashal@kernel.org>

    Uh, rather not release this to stable without the followup fix:
    https://lore.kernel.org/linux-mm/20210504120019.26791-1-vbabka@suse.cz/

    > ---
    > mm/slub.c | 9 +++++++++
    > 1 file changed, 9 insertions(+)
    >
    > diff --git a/mm/slub.c b/mm/slub.c
    > index 05a501b67cd5..e4f7978d43c2 100644
    > --- a/mm/slub.c
    > +++ b/mm/slub.c
    > @@ -3779,6 +3779,15 @@ 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();
    >

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