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Tue, 12 Nov 2024 16:04:04 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id TCrbJ3R8M2dmGQAAD6G6ig (envelope-from ); Tue, 12 Nov 2024 16:04:04 +0000 Date: Tue, 12 Nov 2024 17:04:04 +0100 Message-ID: <874j4ctp57.wl-tiwai@suse.de> From: Takashi Iwai To: Edward Adam Davis Cc: syzbot+73582d08864d8268b6fd@syzkaller.appspotmail.com, linux-kernel@vger.kernel.org, linux-sound@vger.kernel.org, perex@perex.cz, syzkaller-bugs@googlegroups.com, tiwai@suse.com Subject: Re: [PATCH] usb: fix a task hung in snd_card_free In-Reply-To: References: <6726bf35.050a0220.35b515.018b.GAE@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/27.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-sound@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-Rspamd-Queue-Id: DE0B52126C X-Spam-Level: X-Spamd-Result: default: False [-2.01 / 50.00]; BAYES_HAM(-3.00)[99.99%]; SUSPICIOUS_RECIPS(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_CONTAINS_FROM(1.00)[]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; ARC_NA(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FUZZY_BLOCKED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TO_DN_SOME(0.00)[]; FREEMAIL_TO(0.00)[qq.com]; FREEMAIL_ENVRCPT(0.00)[qq.com]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCPT_COUNT_SEVEN(0.00)[7]; TAGGED_RCPT(0.00)[73582d08864d8268b6fd]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[appspotmail.com:email,suse.de:dkim,suse.de:mid,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Rspamd-Action: no action X-Spam-Score: -2.01 X-Spam-Flag: NO On Wed, 06 Nov 2024 03:15:49 +0100, Edward Adam Davis wrote: > > task 1: snd ctrl will add card_dev ref count and can't call close to dec it, > it is blocked waiting for task 2 to release the USB dev lock. > > task 2: usb dev lock has been locked by hung task (here is usb_disconnect), > it is hung waiting for task 1 to exit and release card_dev. > > Adjust the USB lock acquisition method to non-blocking in ioctl to avoid > hang when the USB connection is closed. I'm afraid that this change would break things too badly. i.e. changing the blocking behavior to non-blocking is no-go. > Reported-and-tested-by: syzbot+73582d08864d8268b6fd@syzkaller.appspotmail.com > Closes: https://syzkaller.appspot.com/bug?extid=73582d08864d8268b6fd This particular syzkaller entry can be fixed rather by replacing snd_card_free() in snd_usx2y_disconnect() with snd_card_free_when_closed() like other USB audio drivers, something like below. Judging from the git log, it had been with snd_card_free_in_thread(), but was switch to snd_card_free() around year 2005. Meanwhile the handling of async card release got improved, and it's very likely OK to use snd_card_free_when_closed() there with the recent kernel. thanks, Takashi -- 8< -- --- a/sound/usb/usx2y/usbusx2y.c +++ b/sound/usb/usx2y/usbusx2y.c @@ -422,7 +422,7 @@ static void snd_usx2y_disconnect(struct usb_interface *intf) } if (usx2y->us428ctls_sharedmem) wake_up(&usx2y->us428ctls_wait_queue_head); - snd_card_free(card); + snd_card_free_when_closed(card); } static int snd_usx2y_probe(struct usb_interface *intf,