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Mon, 16 Mar 2026 17:06:34 +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 dRwtJJo4uGloQwAAD6G6ig (envelope-from ); Mon, 16 Mar 2026 17:06:34 +0000 Date: Mon, 16 Mar 2026 18:06:34 +0100 Message-ID: <87jyvb7lgl.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: perex@perex.cz, chleroy@kernel.org, tiwai@suse.com, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, r33s3n6@gmail.com, gality369@gmail.com, zhenghaoran154@gmail.com, hanguidong02@gmail.com, ziyuzhang201@gmail.com Subject: Re: [PATCH v2] ALSA: pcm: oss: use proper stream lock for runtime->state access In-Reply-To: <20260316085047.2876451-1-zzzccc427@gmail.com> References: <20260316085047.2876451-1-zzzccc427@gmail.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 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; 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RCVD_VIA_SMTP_AUTH(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; DKIM_TRACE(0.00)[suse.de:+]; ASN(0.00)[asn:32098, ipnet:2800::/6, country:US]; SPAMHAUS_XBL(0.00)[2a07:de40:b281:104:10:150:64:97:from] X-Rspamd-Queue-Id: EC7335BE1B X-Spam-Flag: NO X-Spam-Score: -3.51 X-Spam-Level: On Mon, 16 Mar 2026 09:50:47 +0100, Cen Zhang wrote: > > __snd_pcm_set_state() writes runtime->state under the PCM stream lock. > However, the OSS I/O functions snd_pcm_oss_write3(), snd_pcm_oss_read3(), > snd_pcm_oss_writev3() and snd_pcm_oss_readv3() read runtime->state > without holding the stream lock, only holding oss.params_lock (a > different mutex that does not synchronize with the stream lock). > > Since __snd_pcm_set_state() is called from IRQ context (e.g., > snd_pcm_period_elapsed -> snd_pcm_update_state -> __snd_pcm_xrun -> > snd_pcm_stop -> snd_pcm_post_stop) while the OSS read/write paths > run in process context, these are concurrent accesses that constitute > a data race. > > Rather than using READ_ONCE()/WRITE_ONCE() barriers, introduce a > snd_pcm_get_state() helper that reads runtime->state under the stream > lock, matching the locking discipline used elsewhere in the PCM layer. > Also export snd_pcm_set_state() for completeness. > > Use snd_pcm_get_state() in all four OSS I/O functions, caching the > result in a local variable where the same snapshot is used for > multiple comparisons to avoid taking the lock repeatedly. > > Signed-off-by: Cen Zhang Applied to for-next branch now. Thanks. Takashi