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Fri, 19 Apr 2024 07:45:29 +0000 (UTC) Received: from dovecot-director2.suse.de ([10.150.64.162]) by imap1.dmz-prg2.suse.org with ESMTPSA id MxorKhkhImavWQAAD6G6ig (envelope-from ); Fri, 19 Apr 2024 07:45:29 +0000 Date: Fri, 19 Apr 2024 09:45:37 +0200 Message-ID: <8734rhvlr2.wl-tiwai@suse.de> From: Takashi Iwai To: Harshit Mogalapalli Cc: Takashi Iwai , Helge Deller , Nam Cao , Thomas Zimmermann , 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: <5febb249-1d4d-4ea7-b031-1df4d14620d2@oracle.com> References: <271372d6-e665-4e7f-b088-dee5f4ab341a@oracle.com> <20240418160652.68df1a86@namcao> <87ttjywxv5.wl-tiwai@suse.de> <878r19voks.wl-tiwai@suse.de> <5febb249-1d4d-4ea7-b031-1df4d14620d2@oracle.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-fbdev@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)[]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; TAGGED_RCPT(0.00)[]; RCPT_COUNT_TWELVE(0.00)[15]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FREEMAIL_ENVRCPT(0.00)[gmail.com,gmx.de]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[suse.de,gmx.de,linutronix.de,ffwll.ch,vger.kernel.org,lists.freedesktop.org,gmail.com,oracle.com,intel.com]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FUZZY_BLOCKED(0.00)[rspamd.com]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] On Fri, 19 Apr 2024 09:39:09 +0200, Harshit Mogalapalli wrote: > > Hi Takashi, > > On 19/04/24 12:14, Takashi Iwai wrote: > > 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. > > > > Thanks for sharing these details. > > > Then later on, the commit 33cd6ea9c067 changed cancel_*() to > > flush_delayed_work() blindly, and the known problem resurfaced again. > > > > I have reverted that commit, but still could see some other task hung > message as shared here on other reply: > > https://lore.kernel.org/all/d2485cb9-277d-4b8e-9794-02f1efababc9@oracle.com/ Yes, then it could be a different cause, I suppose. The crash with flush_delayed_work() was a real crash, no hanging task, IIRC. Can you reproduce the issue with the latest Linus upstream, too? thanks, Takashi