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Wed, 25 Jun 2025 03:00:51 -0700 (PDT) Date: Wed, 25 Jun 2025 18:00:49 +0800 From: Jiazi Li To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, "peixuan.qiu" , Jens Axboe , io-uring@vger.kernel.org Subject: Re: [PATCH] stacktrace: do not trace user stack for user_worker tasks Message-ID: <20250625100049.GA17376@Jiazi.Li> References: <20250623115914.12076-1-jqqlijiazi@gmail.com> <20250624130744.602c5b5f@batman.local.home> Precedence: bulk X-Mailing-List: io-uring@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: <20250624130744.602c5b5f@batman.local.home> User-Agent: Mutt/1.9.4 (2018-02-28) On Tue, Jun 24, 2025 at 01:07:44PM -0400, Steven Rostedt wrote: > On Mon, 23 Jun 2025 19:59:11 +0800 > Jiazi Li wrote: > > > Tasks with PF_USER_WORKER flag also only run in kernel space, > > so do not trace user stack for these tasks. > > What exactly is the difference between PF_KTHREAD and PF_USER_WORKER? > I think that apart from never return to user space, PF_USER_WORKER is basically the same as user space task. > Has all the locations that test for PF_KTHREAD been audited to make > sure that PF_USER_WORKER isn't also needed? > No. > I'm working on other code that needs to differentiate between user > tasks and kernel tasks, and having to have multiple flags to test is > becoming quite a burden. > Yes, so only check both PF_KTHREAD and PF_USER_WORKER before access user space stack? > -- Steve > > > > > > Signed-off-by: Jiazi Li > > Signed-off-by: peixuan.qiu > > --- > > kernel/stacktrace.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/kernel/stacktrace.c b/kernel/stacktrace.c > > index afb3c116da91..82fbccdd1a24 100644 > > --- a/kernel/stacktrace.c > > +++ b/kernel/stacktrace.c > > @@ -228,8 +228,8 @@ unsigned int stack_trace_save_user(unsigned long *store, unsigned int size) > > .size = size, > > }; > > > > - /* Trace user stack if not a kernel thread */ > > - if (current->flags & PF_KTHREAD) > > + /* Skip tasks that do not return to userspace */ > > + if (current->flags & (PF_KTHREAD | PF_USER_WORKER)) > > return 0; > > > > arch_stack_walk_user(consume_entry, &c, task_pt_regs(current)); >