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Fri, 19 Apr 2024 06:44:28 +0000 (UTC) Received: from dovecot-director2.suse.de ([10.150.64.162]) by imap1.dmz-prg2.suse.org with ESMTPSA id d0WbCswSImYIRgAAD6G6ig (envelope-from ); Fri, 19 Apr 2024 06:44:28 +0000 Date: Fri, 19 Apr 2024 08:44:35 +0200 Message-ID: <878r19voks.wl-tiwai@suse.de> From: Takashi Iwai To: Helge Deller Cc: Takashi Iwai , Nam Cao , Thomas Zimmermann , Harshit Mogalapalli , Daniel Vetter , linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, bigeasy@linutronix.de, patrik.r.jakobsson@gmail.com, LKML , Vegard Nossum , George Kennedy , Darren Kenny , chuansheng.liu@intel.com Subject: Re: [bug-report] task info hung problem in fb_deferred_io_work() In-Reply-To: References: <271372d6-e665-4e7f-b088-dee5f4ab341a@oracle.com> <20240418160652.68df1a86@namcao> <87ttjywxv5.wl-tiwai@suse.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-Spam-Flag: NO X-Spam-Score: -1.80 X-Spam-Level: X-Spamd-Result: default: False [-1.80 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TAGGED_RCPT(0.00)[]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_TWELVE(0.00)[15]; FREEMAIL_TO(0.00)[gmx.de]; FREEMAIL_ENVRCPT(0.00)[gmail.com,gmx.de]; FUZZY_BLOCKED(0.00)[rspamd.com]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[suse.de,linutronix.de,oracle.com,ffwll.ch,vger.kernel.org,lists.freedesktop.org,gmail.com,intel.com]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; TO_DN_SOME(0.00)[] On Thu, 18 Apr 2024 21:29:57 +0200, Helge Deller wrote: > > On 4/18/24 16:26, Takashi Iwai wrote: > > On Thu, 18 Apr 2024 16:06:52 +0200, > > Nam Cao wrote: > >> > >> On 2024-04-18 Harshit Mogalapalli wrote: > >>> While fuzzing 5.15.y kernel with Syzkaller, we noticed a INFO: task hung > >>> bug in fb_deferred_io_work() > >> > >> Which framebuffer device are you using exactly? It is possible that > >> the problem is with the device driver, not core framebuffer. > > > > Note that it was already known that using flush_delayed_work() caused > > a problem. See the thread of the fix patch: > > https://lore.kernel.org/all/20230129082856.22113-1-tiwai@suse.de/ > > Harshit reported the hung tasks with kernel v5.15-stable, and can even reproduce > that issue with kernel v6.9-rc4 although it has all of your patches from > that referenced mail thread applied. > So, what does your statement that "it was already known that it causes problems" exactly mean? > Can it be fixed? Is someone looking into fixing it? My original fix was intentionally with cancel_delayed_work_sync() because flush_delayed_work() didn't work. We knew that it'd miss some last-minute queued change, but it's better than crash, so it was applied in that way. Then later on, the commit 33cd6ea9c067 changed cancel_*() to flush_delayed_work() blindly, and the known problem resurfaced again. Takashi