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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-584d12824d7sm521542a12.30.2024.06.27.00.44.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jun 2024 00:44:51 -0700 (PDT) Date: Thu, 27 Jun 2024 09:44:51 +0200 From: Michal Hocko To: alexjlzheng@gmail.com Cc: akpm@linux-foundation.org, brauner@kernel.org, axboe@kernel.dk, oleg@redhat.com, tandersen@netflix.com, willy@infradead.org, mjguzik@gmail.com, alexjlzheng@tencent.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm: optimize the redundant loop of mm_update_next_owner() Message-ID: References: <20240620152744.4038983-1-alexjlzheng@tencent.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20240620152744.4038983-1-alexjlzheng@tencent.com> On Thu 20-06-24 23:27:45, alexjlzheng@gmail.com wrote: > From: Jinliang Zheng > > When mm_update_next_owner() is racing with swapoff (try_to_unuse()) or /proc or > ptrace or page migration (get_task_mm()), it is impossible to find an > appropriate task_struct in the loop whose mm_struct is the same as the target > mm_struct. > > If the above race condition is combined with the stress-ng-zombie and > stress-ng-dup tests, such a long loop can easily cause a Hard Lockup in > write_lock_irq() for tasklist_lock. > > Recognize this situation in advance and exit early. > > Signed-off-by: Jinliang Zheng Even if this is not really a full fix it is a useful stop gap to catch at least some cases. Acked-by: Michal Hocko > --- > Changelog: > > V2: Fix mm_update_owner_next() to mm_update_next_owner() in comment > --- > kernel/exit.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/kernel/exit.c b/kernel/exit.c > index f95a2c1338a8..81fcee45d630 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -484,6 +484,8 @@ void mm_update_next_owner(struct mm_struct *mm) > * Search through everything else, we should not get here often. > */ > for_each_process(g) { > + if (atomic_read(&mm->mm_users) <= 1) > + break; > if (g->flags & PF_KTHREAD) > continue; > for_each_thread(g, c) { > -- > 2.39.3 > -- Michal Hocko SUSE Labs