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Thu, 15 Oct 2026 16:19:06 +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 C6WTEvr80GpeAwAAD6G6ig (envelope-from ); Thu, 15 Oct 2026 16:19:06 +0000 Date: Thu, 15 Oct 2026 18:19:06 +0200 Message-ID: <87h5in6io5.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: Takashi Iwai , perex@perex.cz, tiwai@suse.com, phucduc.bui@gmail.com, cezary.rojewski@intel.com, cassiogabrielcontato@gmail.com, kees+treewide@kernel.org, yilinzhang@moonshot.ai, sammiee5311@gmail.com, kees@kernel.org, thomas.weissschuh@linutronix.de, tglx@kernel.org, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com Subject: Re: [PATCH v2] ALSA: pcm: Unlink substreams before releasing them In-Reply-To: References: <87zewgcuhy.wl-tiwai@suse.de> <87qzhrmnz3.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-Server: rspamd1.dmz-prg2.suse.org X-Rspamd-Queue-Id: 047A421ED3 X-Rspamd-Action: no action X-Spam-Level: X-Spamd-Result: default: False [-3.01 / 50.00]; BAYES_HAM(-3.00)[100.00%]; SUSPICIOUS_RECIPS(1.50)[]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; DWL_DNSWL_LOW(-1.00)[suse.de:dkim]; 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)[]; 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)[17]; 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]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; FREEMAIL_CC(0.00)[suse.de,perex.cz,suse.com,gmail.com,intel.com,kernel.org,moonshot.ai,linutronix.de,vger.kernel.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; TAGGED_RCPT(0.00)[treewide]; 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-Flag: NO X-Spam-Score: -3.01 On Thu, 15 Oct 2026 17:35:30 +0200, Cen Zhang wrote: > > Hi Takashi, > > Takashi Iwai 于2026年10月15日周四 15:18写道： > > > > The patch I submitted yesterday is such an attempt: > > https://lore.kernel.org/20261014141212.316223-1-tiwai@suse.de > > > > Unfortunately it couldn't be reviewed by Sashiko, as it's based on my > > latest tree. And now I noticed that there is still a potential race, > > and fixed now. Will resubmit v2 patch. > > > > > > thanks, > > > > Takashi > > After read the v2 patch. I also have a minor concern: is there still a > lifetime window between snd_refcount_put() and snd_refcount_sync()? > > > Suppose drain(A) has pinned B's runtime, and close(B) has completed > unlink and drop. Could the following happen on two CPUs? > > drain(A) close(B) > -------- -------- > finish_wait(&rt->sleep, &wait); > snd_refcount_put(&rt->refcnt): > decrement count to zero > snd_refcount_sync(&rt->refcnt); > /* sees zero and returns */ > ... > snd_pcm_detach_substream(B); > kfree(rt); > wake_up(&rt->refcnt.waiter); > > Here rt is B's runtime. Since wait_event() can return on its initial > condition check, could the final wake_up() access the embedded > waitqueue after rt has been freed? A holds its own stream lock at > this point, while B has already been unlinked. Yes, and it's covered by another patch: https://lore.kernel.org/20261015112256.3902-1-tiwai@suse.de thanks, Takashi