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Wed, 21 Jan 2026 06:58:42 -0800 (PST) Date: Wed, 21 Jan 2026 09:58:42 -0500 From: Johannes Weiner To: Andrew Morton Cc: Deepanshu Kartikey , syzbot , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, syzkaller-bugs@googlegroups.com, Muchun Song , Minchan Kim , Kairui Song Subject: Re: [syzbot] [cgroups?] [mm?] WARNING in memcg1_swapout Message-ID: References: <696b56b1.050a0220.3390f1.0007.GAE@google.com> <20260117165722.6dc25d72fd58254cb89e711b@linux-foundation.org> <20260118125311.e1894f598e2a8ef626f47f25@linux-foundation.org> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260118125311.e1894f598e2a8ef626f47f25@linux-foundation.org> On Sun, Jan 18, 2026 at 12:53:11PM -0800, Andrew Morton wrote: > On Sun, 18 Jan 2026 12:31:43 +0530 Deepanshu Kartikey wrote: > > > > > > > > > That's > > > > > > > > VM_WARN_ON_ONCE(oldid != 0); > > > > > > > > which was added by Deepanshu's "mm/swap_cgroup: fix kernel BUG in > > > > swap_cgroup_record". > > > > > > > > This patch has Fixes: 1a4e58cce84e ("mm: introduce MADV_PAGEOUT"), > > > > which is six years old. For some reason it has no cc:stable. > > > > > > > > Deepanshu's patch has no reviews. > > > > > > > > So can I please do the memcg maintainer summoning dance here? We have a > > > > repeatable BUG happening in mainline Linux. > > > > > > > > > > Hi Andrew, > > > > > > I checked the git blame output for commit 0f853ca2a798: > > > > > > Line 763: memcg1_swapout(folio, swap); > > > Line 764: __swap_cache_del_folio(ci, folio, swap, shadow); > > > (d7a7b2f91f36b - Kairui Song, 2026-01-13 02:33:36 +0800) > > > > > > Kairui's reordering patch appears to have been merged on Jan 13. > > Eek, there are many patches, it helps to identify them carefully. > > I think you're referring to > https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-swap-use-swap-cache-as-the-swap-in-synchronize-layer-fix.patch This was supposed to be the replacement for Deepanshu's patch below. > > > The syzbot report is also from Jan 13, likely from earlier in the > > > day before the reordering patch was merged. > > > > > > So this report is from before the fix. The warning should not appear > > > in linux-next builds after Jan 13. > > > > > > Thanks, > > > > > > Deepanshu > > > > Hi Andrew, > > > > I tested with the latest linux-next in sysbot. It is working fine > > Great, thanks. But we still don't have review for this one. IOW, this is not necessary anymore. Kairui's (cc'd) fix which you picked up fixed the syzbot reported problem. > For some reason I don't have cc:stable on this - could people > make a recommendation? So this: > From: Deepanshu Kartikey > Subject: mm/swap_cgroup: fix kernel BUG in swap_cgroup_record can be dropped. Please correct if I'm wrong.