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[195.250.132.146]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-584d0c9df6fsm527707a12.6.2024.06.27.00.49.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Jun 2024 00:49:06 -0700 (PDT) Date: Thu, 27 Jun 2024 09:49:05 +0200 From: Michal Hocko To: Oleg Nesterov Cc: Andrew Morton , "Eric W. Biederman" , linux-kernel@vger.kernel.org Subject: Re: [PATCH] get_task_mm: check PF_KTHREAD lockless Message-ID: References: <20240626191017.GA20031@redhat.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: <20240626191017.GA20031@redhat.com> On Wed 26-06-24 21:10:17, Oleg Nesterov wrote: > Nowadays PF_KTHREAD is sticky and it was never protected by ->alloc_lock. > Move the PF_KTHREAD check outside of task_lock() section to make this code > more understandable. > > Signed-off-by: Oleg Nesterov Acked-by: Michal Hocko Thanks! > --- > kernel/fork.c | 11 +++++------ > 1 file changed, 5 insertions(+), 6 deletions(-) > > diff --git a/kernel/fork.c b/kernel/fork.c > index 4c361d2bdc12..d3dc623a1247 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -1536,14 +1536,13 @@ struct mm_struct *get_task_mm(struct task_struct *task) > { > struct mm_struct *mm; > > + if (task->flags & PF_KTHREAD) > + return NULL; > + > task_lock(task); > mm = task->mm; > - if (mm) { > - if (task->flags & PF_KTHREAD) > - mm = NULL; > - else > - mmget(mm); > - } > + if (mm) > + mmget(mm); > task_unlock(task); > return mm; > } > -- > 2.25.1.362.g51ebf55 > -- Michal Hocko SUSE Labs