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Fri, 16 Oct 2026 13:03:00 +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 mWH1BIQg0mo9cAAAD6G6ig (envelope-from ); Fri, 16 Oct 2026 13:03:00 +0000 Date: Fri, 16 Oct 2026 15:02:59 +0200 Message-ID: <87ecdpu7b0.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: Takashi Iwai , perex@perex.cz, tiwai@suse.com, thomas.weissschuh@linutronix.de, kees@kernel.org, phucduc.bui@gmail.com, sammiee5311@gmail.com, clemens@ladisch.de, tglx@kernel.org, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com Subject: Re: [PATCH] ALSA: dummy: Refresh the CD capture switch before use In-Reply-To: References: <87h5iluaqg.wl-tiwai@suse.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 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=ISO-2022-JP X-Rspamd-Action: no action X-Spam-Score: -2.01 X-Spam-Flag: NO X-Spamd-Result: default: False [-2.01 / 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]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCPT_COUNT_TWELVE(0.00)[14]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; FREEMAIL_CC(0.00)[suse.de,perex.cz,suse.com,linutronix.de,kernel.org,gmail.com,ladisch.de,vger.kernel.org]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:104:10:150:64:97:from]; TAGGED_RCPT(0.00)[]; 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)[suse.de:email,suse.de:dkim,imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns] X-Spam-Level: X-Rspamd-Queue-Id: BBCD01F397 X-Rspamd-Server: rspamd2.dmz-prg2.suse.org On Fri, 16 Oct 2026 14:50:04 +0200, Cen Zhang wrote: > > Hi Takashi, > > Takashi Iwai 于2026年10月16日周五 19:49写道： > > > > On Fri, 16 Oct 2026 04:01:10 +0200, > > Cen Zhang wrote: > > > > > > The CD Capture Switch control must remain live while > > > snd_dummy_iobox_put() updates its access flags and uses its ID for > > > notification. snd_card_dummy_new_mixer() caches the control pointer, but > > > snd_ctl_remove_id() can unlink and free it without updating that cache. > > > > > > This requires a kernel caller to remove the switch while the dummy card > > > stays connected and External I/O Box remains writable. Userspace > > > ELEM_REMOVE rejects this driver control because it lacks > > > SNDRV_CTL_ELEM_ACCESS_USER. > > > > So, the removal shouldn't happen, but... > > > > > With I/O Box initially 1 and CD Volume still > > > present, the following ordered sequence is possible: > > > > > > 1. snd_ctl_remove_id() takes controls_rwsem for write, finds and > > > unlinks CD Capture Switch, sends removal notifications and calls > > > snd_ctl_free_one(), then drops the semaphore and returns. > > > > ... how this happens at all? Unless 1 really happens, the rest are > > fictional dreams. > > > > The same for another dummy driver patch. Does it really happen at > > all? > > > > > > thanks, > > > > Takashi > > Thanks very much for the review. You're right. It is AI obfuscation. > After carefully checking the code myself, I could not find a real path > that removes them. > > I'm very, very sorry for this noise. Please disregard both patches. > I'll be much more careful in the future. Don't worry, your patches have been appreciated. But, I guess that we can ask the model to provide a PoC code for triggering the bug, at least for the case like dummy driver, and verify the actual crash? This would show more clearly whether it's a real issue or not. thanks, Takashi