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Thu, 29 Jan 2026 02:09:02 -0800 (PST) From: Richard Weinberger To: Richard Weinberger , xenomai@lists.linux.dev, upstream@sigma-star.at, Jan Kiszka Cc: upstream+xenomai@sigma-star.at Subject: Re: [PATCH] Fix race between RTDM task termination and xnthread_join Date: Thu, 29 Jan 2026 11:09:02 +0100 Message-ID: <9873549.lNWL4n7ouV@nailgun> In-Reply-To: <64c4befa-111c-43c4-ba24-5f079e17c4c7@siemens.com> References: <20260127213927.26960-1-richard@nod.at> <3506084.tBmWVcJkqe@nailgun> <64c4befa-111c-43c4-ba24-5f079e17c4c7@siemens.com> Precedence: bulk X-Mailing-List: xenomai@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" On Donnerstag, 29. J=C3=A4nner 2026 10:57 Jan Kiszka wrote: > On 29.01.26 09:36, Richard Weinberger wrote: > > On Donnerstag, 29. J=C3=A4nner 2026 08:45 'Jan Kiszka' via upstream wro= te: > >> On 27.01.26 22:39, Richard Weinberger wrote: > >>> Ensure that the task structure remains valid until the join operation= is complete. > >>> Previously, a race condition could cause the structure to be freed be= fore > >>> xnthread_join() accessed it, leading to a use-after-free scenario. > >> > >> Where exactly? xnthread_join performs some checks for the existence of > >> the target, and it is locking it (find_get_pid). > >=20 > > xnthread_host_pid() in xnthread_join() dereferences the task struct via > > task_pid_nr(). >=20 > Then then next question would be what is protecting the task struct in > case of userspace task. Is this here only papering over a more > fundamental issue? Hmm, for userspace I'd expect that Linux frees the task struct only after the parent fetched the exit code? So, after zombie state. Thanks, //richard =2D-=20 =E2=80=8B=E2=80=8B=E2=80=8B=E2=80=8B=E2=80=8Bsigma star gmbh | Eduard-Bodem= =2DGasse 6, 6020 Innsbruck, AUT UID/VAT Nr: ATU 66964118 | FN: 374287y