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

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Date:   Wed, 12 May 2021 19:25:24 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Oliver Glitta <glittao@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 518/530] mm, slub: enable slub_debug static key when
 creating cache with explicit debug flags

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@...e.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@...e.cz>
>> > Reported-by: Oliver Glitta <glittao@...il.com>
>> > Acked-by: David Rientjes <rientjes@...gle.com>
>> > Cc: Christoph Lameter <cl@...ux.com>
>> > Cc: Pekka Enberg <penberg@...nel.org>
>> > Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
>> > Cc: "Paul E. McKenney" <paulmck@...nel.org>
>> > Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>> > Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
>> > Signed-off-by: Sasha Levin <sashal@...nel.org>
>> 
>> Uh, rather not release this to stable without the followup fix:
>> https://lore.kernel.org/linux-mm/20210504120019.26791-1-vbabka@suse.cz/
> 
> 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.

> thanks,
> 
> greg k-h
>