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b=LUxB4Wpy4M0NA/auUkF3ugzHwzl9yI2Akd18tG6e7Wd+FVpo90FHoQkUmsjoQ/CZ2 47peU4JJ7n84TwVTZASc2hIZ/h6OQcE2VP1/G6MGlMPX7WOM5E4NhtGonekT2SkXTa Qku9hWMU1SUQBG3UKn33NnZ6lMWsvhSV/SkGi++l/LCHLkmqGAev1nHip9ImhXkScT ZnyBGlx5fLgOuTbOwAVTpLlpHSqlKtNv2DtqwnTw7PidO8LFLEJi4xvLhGK7AxH68x 9BI98yhjX34QdpVDlC012GsUwaPtRA2Y+Kp3PdC0Tm3amFXF+Q55wdEwtRGUVBNjSE IPmaM1qdncb3Q== Date: Tue, 13 Oct 2026 15:29:11 +0100 From: Harry Yoo To: Imre Kaloz Cc: Vlastimil Babka , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/slab: sample slab_state once in kmem_cache_destroy() Message-ID: References: <20260930195110.13296-1-kaloz@kernel.org> <481e9a16-cd30-d463-14ee-b5602bcd5a21@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <481e9a16-cd30-d463-14ee-b5602bcd5a21@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: DAD724000A X-Stat-Signature: tajje5e8zwmj9d18t443zeyecafz6d15 X-HE-Tag: 1791901754-918905 X-HE-Meta: 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 nPqbDq53 gMjTMODz+DgccH4B2UtwAXZ45kJV5qIiYwkv8gWTgA7g1LpGC6inEUNtt9SYso9DX6mvm7Q8MpVRAB0gSzLz/xfUIUOY9H8v15dLgkky/YLNNhxOhmgBDS81kvpwu3LXDeUxylEWfy79I+i8+JIEVTzTnO2LAMCFLgVQVGp1/IdpYGFO/scfVn7357u8TXFbxy2Hm8qg07XsaBHGIlp0oeae9t0+eYOCrSyzQLKwUn4KwPheHbj4YG0JinZrf6Mj0m4dTQOMTdusI9jlSiuC+9Gh5zHY82sKQJMut4ba4hFUOGMk= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Oct 13, 2026 at 02:51:30PM +0200, Imre Kaloz wrote: > Hi Harry, Hi Imre, > On Tue, 13 Oct 2026, Harry Yoo wrote: > > > Uh, apologies for the late reply. > > Catching up after trip at LPC... > > No worries, hope LPC was good! Thanks. It was good. > > On Thu, Oct 01, 2026 at 05:42:36PM +0200, Imre Kaloz wrote: > > > > > > There is a related older window: after list_del() and before that > > > single read, slab_sysfs_init() could set FULL, skip this cache, and > > > the single read would then call both unlink and release on an > > > uninitialized kobject. > > > > No, with this patch slab_sysfs_init() cannot set the state to FULL > > because the slab_caches list and slab_state are protected by slab_mutex. > > > > > I have not hit that, and this patch does not close it. > > > > I think the patch does close two bugs. > > > > One introduced by 4ec10268ed98 (reading slab_state twice), > > another (reading slab_state outside slab_mutex) introduced by, hmm, > > not sure which commit introduced it :) should be very old. > > You're right, I got that one wrong. Sampling under slab_mutex in the > same section as the list_del() means slab_late_init() either sees the > cache on the list or we see slab_state < FULL, so the older window is > closed too. > > As for where the outside-mutex read came from, as far as I can tell it's > 0495e337b703 ("mm/slab_common: Deleting kobject in kmem_cache_destroy() > without holding slab_mutex/cpu_hotplug_lock"). Before that, the unlink > and release and their slab_state checks ran in shutdown_cache() under > slab_mutex. 0495e337b703 Probably yes. Not 100% sure. It's quite messy, reading slab_state has been done inside, switched to outside, and back to inside, and so on. But should be fine as long as we can find the first commit that affects -stable kernels (>= 5.10.y) > SLAB_TYPESAFE_BY_RCU caches were already released from the > workfn outside the mutex since 657dc2f97220. > > Want me to send a v2 with a second Fixes: for 0495e337b703, or is it > fine to add it when applying? Could you please verify fixing which bugs resolves the issue on sparc64 described in the changelog? Reading it twice, or outside slab_mutex, or both? -- Cheers, Harry / Hyeonggon