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Mon, 14 Sep 2026 23:57:02 -0700 (PDT) Date: Tue, 15 Sep 2026 08:57:01 +0200 From: Michal Hocko To: Andrew Morton Cc: Jiayuan Chen , linux-mm@kvack.org, Jiayuan Chen , Zhou Yingfu , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , David Rientjes , Shakeel Butt , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/oom_kill: fix hung tasks queued on mmap_lock behind a long reap Message-ID: References: <20260914113239.367200-1-jiayuan.chen@linux.dev> <20260914203533.3544ae8dd0903c7603b385c6@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260914203533.3544ae8dd0903c7603b385c6@linux-foundation.org> X-Rspam-User: X-Stat-Signature: dygigpty3pgnk4s8so7hn33cjwgomejc X-Rspamd-Queue-Id: 52468A0008 X-Rspamd-Server: rspam07 X-HE-Tag: 1789455424-785520 X-HE-Meta: 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 Cun0ZPID 6PbR3kkxwGPyUQ3fmxazM0AEC2IXCVJD8Rr5tu4w1wu3GsH8EO/D0+SH4K4L+WVCKf7CcoiwG8Y+LFQlQWWUdBik4ms4QTF/67qtbw7lZV8m2e7lUhgoc32XkBXFRjTYvs1I0W/TiT42P7aTa3qkrwH4GKVSBhncpAtMR70H9NB3ZXrMEhKVNi02c4dnNHkzspBOZeg9vX5R0PJdKAEfFcDhoANDMD2uEhEGbukm0j1FFhr2Fr/KweNbPvI8gjrhWtkFmY4RMmHjaqfo4v8AXXMaqZuMIQFRVa5GNl5DqN5fIbbBZV7LghbWB3hQlHb7r5bWtiuZOSKO+oLJvQmH4qf6pRdm3IVnWHNIcGVaolNtlaRSiXM+VWJZANNvtaPyoY4W7LnmkXMOxdLe2YR5BeQBil91JwdaBVVRSIIbUn9/cOpJ5V6shJ4pul3e8BcgN6wGRNdVpo/YrBkdvx1+S7gKRRw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon 14-09-26 20:35:33, Andrew Morton wrote: > On Mon, 14 Sep 2026 20:36:16 +0200 Michal Hocko wrote: > > > > Call Trace: > > > > > > __schedule+0x487/0x1870 > > > schedule+0x28/0xb0 > > > schedule_preempt_disabled+0x16/0x30 > > > rwsem_down_write_slowpath+0x1d4/0x750 > > > down_write+0x60/0x70 > > > __ksm_exit+0xb4/0x230 > > > __mmput+0x12c/0x150 > > > mmput+0x1e/0x30 > > > do_exit+0x283/0xa30 > > > do_group_exit+0x34/0x90 > > > get_signal+0x952/0x960 > > > arch_do_signal_or_restart+0x41/0x250 > > > exit_to_user_mode_loop+0xd3/0x560 > > > do_syscall_64+0x385/0x470 > > > > > > > > > KSM is just the one LTP happened to hit: __khugepaged_exit() has the > > > same write lock cycle ahead of exit_mmap(). > > > > Why is this a practical problem we need to care about? It is kind of > > natural that the oom victim exit path might race with the oom reaper. They > > share the same lock that is mutualy exclusive. The whole point of the > > reaper is to ensure there is a forward progress achieved. So before we > > start modifying this let's talk about any practical/real life problems. > > If this situation is expected, unavoidable etc then perhaps the best > change is to periodically poke the hung-task detector? Right. Reaping 10s of GBs worth of VMAs might take some time indeed and that could trigger the hung task detector. -- Michal Hocko SUSE Labs