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Thu, 22 Oct 2026 11:08:55 +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 YOJfGMfu2WpiVQAAD6G6ig (envelope-from ); Thu, 22 Oct 2026 11:08:55 +0000 Date: Thu, 22 Oct 2026 13:08:55 +0200 Message-ID: <87h5iec7qw.wl-tiwai@suse.de> From: Takashi Iwai To: Cen Zhang Cc: Takashi Iwai , perex@perex.cz, tiwai@suse.com, linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org, baijiaju1990@gmail.com, jjzuming@gmail.com Subject: Re: [PATCH] ALSA: pcm: Drain proc writers before freeing preallocated buffers In-Reply-To: References: <87h5igix41.wl-tiwai@suse.de> <87v76uccta.wl-tiwai@suse.de> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: 8bit X-Spam-Flag: NO X-Spam-Level: X-Spamd-Result: default: False [-12.30 / 50.00]; SUSE_INTERNAL_BYPASS(-9.00)[]; BAYES_HAM(-3.00)[100.00%]; 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]; RCVD_TLS_ALL(0.00)[]; TO_DN_SOME(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; RCVD_VIA_SMTP_AUTH(0.00)[]; FREEMAIL_TO(0.00)[gmail.com]; FREEMAIL_ENVRCPT(0.00)[gmail.com]; 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,perex.cz,suse.com,vger.kernel.org,gmail.com]; RCPT_COUNT_SEVEN(0.00)[8]; FROM_EQ_ENVFROM(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,suse.de:email] X-Spam-Score: -12.30 On Thu, 22 Oct 2026 12:56:37 +0200, Cen Zhang wrote: > > Takashi Iwai 于2026年10月22日周四 17:19写道： > > > > On Thu, 22 Oct 2026 10:58:02 +0200, > > Cen Zhang wrote: > > > > > > Hi Takashi, > > > > > > Takashi Iwai 于2026年10月20日周二 16:40写道： > > > > > > > > I believe a better fix is to handle the disconnection of procfs more > > > > properly. The hda codec driver calls snd_device_disconnect() for each > > > > pcm, but in the PCM side, the procfs removal relies on the card level > > > > disconnection (snd_info_card_disconnect()). > > > > > > > > That is, something like below works instead? > > > > > > > > > > > > thanks, > > > > > > > > Takashi > > > > > > > > --- a/sound/core/pcm.c > > > > +++ b/sound/core/pcm.c > > > > @@ -1119,6 +1119,7 @@ static int snd_pcm_dev_disconnect(struct snd_device *device) > > > > for (cidx = 0; cidx < 2; cidx++) { > > > > if (pcm->streams[cidx].dev) > > > > snd_unregister_device(pcm->streams[cidx].dev); > > > > + snd_pcm_stream_proc_done(&pcm->streams[cidx]); > > > > free_chmap(&pcm->streams[cidx]); > > > > } > > > > return 0; > > > > > > > > > > Sorry for the delayed reply — something came up to me over the past > > > few days. > > > > > > Thanks for the review. Handling the proc entries at PCM disconnect > > > looks like a better approach.But I noticed two possible issues with > > > adding the call here: proc removal can invoke a prealloc release > > > callback that takes open_mutex, which is already held; freeing the > > > subtree also leaves pstr->oss.proc_entry pointing to freed storage > > > until final unregister. > > > > Hm, basically we don't have to release the resources but just > > disconnect procfs (that guarantees that the pending callbacks are > > finished). So how about something like below instead? > > > > > I'll follow your approach, but perform proc rundown outside open_mutex > > > and retain the entry objects until final cleanup. I'll also prevent subsequent > > > card registration from republishing the disconnected entries. > > > > But those are assumptions: the proc rundown must be after all pending > > stuff is gone and it shouldn't be called until the next registration. > > And, running re-registering before the complete release is already > > fundamentally broken, and that should be addressed instead. > > > > > > thanks, > > > > Takashi > > > > -- 8< -- > > diff --git a/include/sound/info.h b/include/sound/info.h > > index adbc506860d6..4b08a32ff4fe 100644 > > --- a/include/sound/info.h > > +++ b/include/sound/info.h > > @@ -117,6 +117,7 @@ struct snd_info_entry *snd_info_create_module_entry(struct module *module, > > struct snd_info_entry *snd_info_create_card_entry(struct snd_card *card, > > const char *name, > > struct snd_info_entry *parent); > > +void snd_info_disconnect_entry(struct snd_info_entry *entry); > > void snd_info_free_entry(struct snd_info_entry *entry); > > > > int snd_info_card_create(struct snd_card *card); > > diff --git a/sound/core/info.c b/sound/core/info.c > > index c4d57d0809ad..bb9f564001ea 100644 > > --- a/sound/core/info.c > > +++ b/sound/core/info.c > > @@ -737,6 +737,15 @@ static void snd_info_clear_entries(struct snd_info_entry *entry) > > entry->p = NULL; > > } > > > > +void snd_info_disconnect_entry(struct snd_info_entry *entry) > > +{ > > + if (entry && entry->p) { > > + proc_remove(entry->p); > > + guard(mutex)(&info_mutex); > > + snd_info_clear_entries(entry); > > + } > > +} > > + > > /** > > * snd_info_free_entry - release the info entry > > * @entry: the info entry > > @@ -749,11 +758,7 @@ void snd_info_free_entry(struct snd_info_entry * entry) > > > > if (!entry) > > return; > > - if (entry->p) { > > - proc_remove(entry->p); > > - guard(mutex)(&info_mutex); > > - snd_info_clear_entries(entry); > > - } > > + snd_info_disconnect_entry(entry); > > > > /* free all children at first */ > > list_for_each_entry_safe(p, n, &entry->children, list) > > diff --git a/sound/core/pcm.c b/sound/core/pcm.c > > index 1e4e0ecb3dbd..58098ee894a1 100644 > > --- a/sound/core/pcm.c > > +++ b/sound/core/pcm.c > > @@ -520,6 +520,11 @@ static int snd_pcm_stream_proc_init(struct snd_pcm_str *pstr) > > return 0; > > } > > > > +static void snd_pcm_stream_proc_disconnect(struct snd_pcm_str *pstr) > > +{ > > + snd_info_disconnect_entry(pstr->proc_root); > > +} > > + > > static int snd_pcm_stream_proc_done(struct snd_pcm_str *pstr) > > { > > snd_info_free_entry(pstr->proc_root); > > @@ -580,6 +585,7 @@ static int snd_pcm_substream_proc_init(struct snd_pcm_substream *substream) > > > > #else /* !CONFIG_SND_VERBOSE_PROCFS */ > > static inline int snd_pcm_stream_proc_init(struct snd_pcm_str *pstr) { return 0; } > > +static inline void snd_pcm_stream_proc_disconnect(struct snd_pcm_str *pstr) { return 0; } > > static inline int snd_pcm_stream_proc_done(struct snd_pcm_str *pstr) { return 0; } > > static inline int snd_pcm_substream_proc_init(struct snd_pcm_substream *substream) { return 0; } > > #endif /* CONFIG_SND_VERBOSE_PROCFS */ > > @@ -1119,6 +1125,7 @@ static int snd_pcm_dev_disconnect(struct snd_device *device) > > for (cidx = 0; cidx < 2; cidx++) { > > if (pcm->streams[cidx].dev) > > snd_unregister_device(pcm->streams[cidx].dev); > > + snd_pcm_stream_proc_disconnect(&pcm->streams[cidx]); > > free_chmap(&pcm->streams[cidx]); > > } > > return 0; > > Agree that. But I moved proc rundown outside open_mutex because > proc_remove() can invoke the > prealloc release callback, which takes that mutex. OK, it makes sense. Takashi