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Mercier" Cc: Michal Hocko , hannes@cmpxchg.org, roman.gushchin@linux.dev, muchun.song@linux.dev, zhengqi.arch@bytedance.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm: memcontrol: fix NULL pointer deref in high_work_func() on dying memcg Message-ID: References: <20261023222313.3979455-1-tjmercier@google.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: D295AC0002 X-Stat-Signature: 635sfcc55dkweghfpqun9nyppc9rpiat X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspam-User: X-HE-Tag: 1793124437-133632 X-HE-Meta: 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 kQzlbLOE LDVQruN3QR7qmjRXQFX/8RuYA1c8dCmneQtyQQuF491ZJNakYxmZDYzJf9VM/5tCVKB4HjAzhX5gtVcgXvYZ6ezUCVJXRNzqYSdaRQUf2WkaNWdW7XluaMXMjvt5f0lRRA6rxYSA391oWQLZVWrtOoRdXXIjkJiTxvMcOaYpwdiaG12rpmMEBRaL6keENweayQRmmEASw/Evfr8j+KG0EV0UeXCSiQlnaRTiMs/pVFcoiITSuUU5mVkdmDzi4k6kzgqm5slsvSX+jdZ1M7PHAkUk3Ld3zlo2ioEjM0nfmbr2Z03MPF1zSMETre2BvBqCY6hq10AZYe854lSSQsD8+MkU3MiCOCp5L9XfuMdBX889DtG9iWIm5voFFusU20RUbzuYSSgER7+g+ANnOfCDNxBbDUA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Tue, Oct 27, 2026 at 10:28:22AM -0700, T.J. Mercier wrote: > On Tue, Oct 27, 2026 at 2:41 AM Michal Hocko wrote: > > > > On Mon 26-10-26 11:01:51, T.J. Mercier wrote: > > > On Mon, Oct 26, 2026 at 6:25 AM Michal Hocko wrote: > > > > [...] > > > > On Fri 23-10-26 15:23:13, T.J. Mercier wrote: > > I must be missing something really obvious here because I really do not > > follow you here too. So we are offlining a memcg. We need to coordinate > > memory reclaim with the memcg tear down, right? For the high reclaim we > > can achieve this synchronization through disable_work_sync in > > mem_cgroup_css_offline. > > We could call disable_work_sync() in mem_cgroup_css_offline(), but > that waits until high_work_func() is done and it could be performing > reclaim. mem_cgroup_css_offline() runs under the cgroup_mutex, and > cgroup_mutex contention is already bad enough. I don't want to add to > it. It would also block the rest of the cgroup_offline_wq. +1, let's not add more potential contention sources for cgroup_mutex.