Re: [PATCH 5.10 518/530] mm, slub: enable slub_debug static key when creating cache with explicit debug flags

[Sasha Levin]

On Wed, May 12, 2021 at 07:25:24PM +0200, Vlastimil Babka wrote:
> On 5/12/21 5:50 PM, Greg Kroah-Hartman wrote:
> > On Wed, May 12, 2021 at 05:35:28PM +0200, Vlastimil Babka wrote:
> > > On 5/12/21 4:50 PM, Greg Kroah-Hartman wrote:
> > > > From: Vlastimil Babka <vbabka@xxxxxxx>
> > > >
> > > > [ 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@xxxxxxxx/
> > > >
> > > > Link: https://lkml.kernel.org/r/20210315153415.24404-1-vbabka@xxxxxxx
> > > > Fixes: ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()")
> > > > Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> > > > Reported-by: Oliver Glitta <glittao@xxxxxxxxx>
> > > > Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
> > > > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > > > Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> > > > Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > > > Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> > > > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
> > >
> > > Uh, rather not release this to stable without the followup fix:
> > > https://lore.kernel.org/linux-mm/20210504120019.26791-1-vbabka@xxxxxxx/
> >
> > Is that in Linus's tree yet?  If so, what is the git id?
>
> No, it's in mmotm, so no git id yet, but should make it to Linus during 5.13 rc's.

I'll drop it for now, thanks!

--
Thanks,
Sasha