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Mon, 13 Jul 2026 06:49:56 -0700 (PDT) Date: Mon, 13 Jul 2026 14:49:55 +0100 From: Matt Fleming To: Tejun Heo Cc: David Vernet , Andrea Righi , Changwoo Min , Johannes Weiner , Suren Baghdasaryan , Peter Zijlstra , Edward Adam Davis , Chen Ridong , Zhaoyang Huang , "ziwei . dai" , "ke . wang" , Matt Fleming , sched-ext@lists.linux.dev, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@cloudflare.com Subject: Re: [PATCHSET v2] sched/psi: Fix psimon fork deadlock and rtpoll_timer UAF Message-ID: References: <20260712174619.3553231-1-tj@kernel.org> Precedence: bulk X-Mailing-List: sched-ext@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260712174619.3553231-1-tj@kernel.org> On Sun, Jul 12, 2026 at 07:46:17AM -1000, Tejun Heo wrote: > Hello, > > v2: - Retagged sched/psi (was cgroup) (patch 1). > - Added a fix for a pre-existing rtpoll_timer use-after-free that the > Sashiko AI review flagged on the previous posting (patch 2). > > v1: https://lore.kernel.org/r/20260710134945-psimon-fix-tj@kernel.org > > a5b98009f16d ("sched/psi: fix race between file release and pressure > write") made pressure_write() fork the psimon kthread while holding > cgroup_mutex, which deadlocks against the sched_ext enable path blocking > forks before grabbing cgroup_mutex. Patch 1 moves the fork outside > cgroup_mutex. Patch 2 fixes the use-after-free from a schedule attempt > re-arming group->rtpoll_timer behind psi_trigger_destroy() by shutting > down the timer when the group is freed. > > Matt, patch 1 is unchanged from the previous posting except for the > subject prefix, so test results against that posting still apply. I ended up testing both patches. This resolves the issue for me! Thanks, Matt