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Mon, 12 Jan 2026 07:27:12 -0800 (PST) Received: from localhost ([2603:7000:c01:2716:365a:60ff:fe62:ff29]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8c37f4a97fesm1512326085a.4.2026.01.12.07.27.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jan 2026 07:27:11 -0800 (PST) Date: Mon, 12 Jan 2026 10:27:07 -0500 From: Johannes Weiner To: Deepanshu Kartikey Cc: mhocko@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, syzbot+d97580a8cceb9b03c13e@syzkaller.appspotmail.com, Kairui Song Subject: Re: [PATCH] mm/swap_cgroup: fix kernel BUG in swap_cgroup_record Message-ID: References: <20260110064613.606532-1-kartikey406@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260110064613.606532-1-kartikey406@gmail.com> X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 2ABE84000B X-Stat-Signature: rfstn4aa4bkaycxsij49jk1wmw38o84g X-Rspam-User: X-HE-Tag: 1768231632-217785 X-HE-Meta: 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 tpOKmRSc 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Jan 10, 2026 at 12:16:13PM +0530, Deepanshu Kartikey wrote: > When using MADV_PAGEOUT, pages can remain in swapcache with their swap > entries assigned. If MADV_PAGEOUT is called again on these pages, This doesn't add up to me - maybe I'm missing something. memcg1_swapout() is called at the very end of reclaim, from __remove_mapping(), which *removes the folio from swapcache*. At this point the folio is exclusive to *that* thread - there are no more present ptes that another madvise could even be acting on. How could we reach here twice for the same swap entry? It seems more likely that we're missing a swapin notification, fail to clear the swap entry from the cgroup records, and then trip up when the entry is recycled to a totally different page down the line. No?