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[87.106.108.193]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43970d3ff27sm27378080f8f.22.2026.02.24.02.00.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 24 Feb 2026 02:00:56 -0800 (PST) Date: Tue, 24 Feb 2026 11:00:42 +0100 From: =?iso-8859-1?Q?G=FCnther?= Noack To: Hillf Danton Cc: syzbot , linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com Subject: Re: [syzbot] [kernel?] INFO: task hung in restrict_one_thread_callback Message-ID: <20260224.a1716faa25c1@gnoack.org> References: <69984159.050a0220.21cd75.01bb.GAE@google.com> <20260224001031.3441-1-hdanton@sina.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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260224001031.3441-1-hdanton@sina.com> On Tue, Feb 24, 2026 at 08:10:30AM +0800, Hillf Danton wrote: > On Fri, Feb 20, 2026 at 03:11:21AM -0800 > > Hello, > > > > syzbot found the following issue on: > > > > HEAD commit: 635c467cc14e Add linux-next specific files for 20260213 > > git tree: linux-next > > console output: https://syzkaller.appspot.com/x/log.txt?x=1452f6e6580000 > > kernel config: https://syzkaller.appspot.com/x/.config?x=61690c38d1398936 > > dashboard link: https://syzkaller.appspot.com/bug?extid=7ea2f5e9dfd468201817 > > compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8 > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16e41c02580000 > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15813652580000 > > #syz test > > --- x/security/landlock/tsync.c > +++ y/security/landlock/tsync.c > @@ -540,11 +540,8 @@ int landlock_restrict_sibling_threads(co > * of for_each_thread(). We can reset it on each loop iteration because > * all previous loop iterations are done with it already. > * > - * num_preparing is initialized to 1 so that the counter can not go to 0 > - * and mark the completion as done before all task works are registered. > - * We decrement it at the end of the loop body. > */ > - atomic_set(&shared_ctx.num_preparing, 1); > + atomic_set(&shared_ctx.num_preparing, 0); > reinit_completion(&shared_ctx.all_prepared); > > /* > @@ -553,11 +550,7 @@ int landlock_restrict_sibling_threads(co > */ > found_more_threads = schedule_task_work(&works, &shared_ctx); > > - /* > - * Decrement num_preparing for current, to undo that we initialized it > - * to 1 a few lines above. > - */ > - if (atomic_dec_return(&shared_ctx.num_preparing) > 0) { > + if (atomic_read(&shared_ctx.num_preparing) > 0) { > if (wait_for_completion_interruptible( > &shared_ctx.all_prepared)) { > /* In case of interruption, we need to retry the system call. */ > -- Hello Hillf! Thanks for your contribution; We have already analyzed the bug on an adjacent mail thread and have a tentative patch of which we know it'll fix the issue: https://lore.kernel.org/all/20260224062729.2908692-1-dingyihan@uniontech.com/ –Günther