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From: Ben Russell <thematrixeatsyou@gmail.com>
To: alsa-devel@alsa-project.org
Cc: Ben Russell <thematrixeatsyou@gmail.com>
Subject: [alsa-devel] [PATCH 2/3] pcm_ioplug: Don't unlock+lock if we're not locked
Date: Sun, 22 Sep 2019 15:28:52 +1200	[thread overview]
Message-ID: <20190922032853.6123-3-thematrixeatsyou@gmail.com> (raw)
In-Reply-To: <20190922032853.6123-1-thematrixeatsyou@gmail.com>

This fixes a deadlock when using the pcm_jack plugin via a plug.

Some snd_pcm_ioplug_* functions assumed that they were being
called with the pcm mutex locked, and would perform an
unlock-act-lock sequence in order to allow the relevant function to
lock the mutex itself.

If the mutex was not locked before calling these functions, it
would silently fail on unlocking the mutex, and then erroneously
leave the mutex locked as it left the function.

This patch checks to see if the mutex is locked before attempting
the unlock-act-lock sequence. If the mutex is not locked when
entering these functions, then we act and leave the mutex unlocked.

Signed-off-by: Ben Russell <thematrixeatsyou@gmail.com>
---
 src/pcm/pcm_ioplug.c | 50 +++++++++++++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 15 deletions(-)

diff --git a/src/pcm/pcm_ioplug.c b/src/pcm/pcm_ioplug.c
index a437ca32..a94ecd96 100644
--- a/src/pcm/pcm_ioplug.c
+++ b/src/pcm/pcm_ioplug.c
@@ -164,9 +164,13 @@ static int snd_pcm_ioplug_prepare(snd_pcm_t *pcm)
 
 	snd_pcm_ioplug_reset(pcm);
 	if (io->data->callback->prepare) {
-		snd_pcm_unlock(pcm); /* to avoid deadlock */
-		err = io->data->callback->prepare(io->data);
-		snd_pcm_lock(pcm);
+		if (snd_pcm_is_locked(pcm)) {
+			snd_pcm_unlock(pcm); /* to avoid deadlock */
+			err = io->data->callback->prepare(io->data);
+			snd_pcm_lock(pcm);
+		} else {
+			err = io->data->callback->prepare(io->data);
+		}
 	}
 	if (err < 0)
 		return err;
@@ -463,9 +467,13 @@ static int snd_pcm_ioplug_sw_params(snd_pcm_t *pcm, snd_pcm_sw_params_t *params)
 	if (!io->data->callback->sw_params)
 		return 0;
 
-	snd_pcm_unlock(pcm); /* to avoid deadlock */
-	err = io->data->callback->sw_params(io->data, params);
-	snd_pcm_lock(pcm);
+	if (snd_pcm_is_locked(pcm)) {
+		snd_pcm_unlock(pcm); /* to avoid deadlock */
+		err = io->data->callback->sw_params(io->data, params);
+		snd_pcm_lock(pcm);
+	} else {
+		err = io->data->callback->sw_params(io->data, params);
+	}
 
 	return err;
 }
@@ -764,9 +772,13 @@ static int snd_pcm_ioplug_poll_descriptors_count(snd_pcm_t *pcm)
 	int err = 1;
 
 	if (io->data->callback->poll_descriptors_count) {
-		snd_pcm_unlock(pcm); /* to avoid deadlock */
-		err = io->data->callback->poll_descriptors_count(io->data);
-		snd_pcm_lock(pcm);
+		if (snd_pcm_is_locked(pcm)) {
+			snd_pcm_unlock(pcm); /* to avoid deadlock */
+			err = io->data->callback->poll_descriptors_count(io->data);
+			snd_pcm_lock(pcm);
+		} else {
+			err = io->data->callback->poll_descriptors_count(io->data);
+		}
 	}
 	return err;
 }
@@ -777,9 +789,13 @@ static int snd_pcm_ioplug_poll_descriptors(snd_pcm_t *pcm, struct pollfd *pfds,
 	int err;
 
 	if (io->data->callback->poll_descriptors) {
-		snd_pcm_unlock(pcm); /* to avoid deadlock */
-		err = io->data->callback->poll_descriptors(io->data, pfds, space);
-		snd_pcm_lock(pcm);
+		if (snd_pcm_is_locked(pcm)) {
+			snd_pcm_unlock(pcm); /* to avoid deadlock */
+			err = io->data->callback->poll_descriptors(io->data, pfds, space);
+			snd_pcm_lock(pcm);
+		} else {
+			err = io->data->callback->poll_descriptors(io->data, pfds, space);
+		}
 		return err;
 	}
 	if (pcm->poll_fd < 0)
@@ -799,9 +815,13 @@ static int snd_pcm_ioplug_poll_revents(snd_pcm_t *pcm, struct pollfd *pfds, unsi
 	int err;
 
 	if (io->data->callback->poll_revents) {
-		snd_pcm_unlock(pcm); /* to avoid deadlock */
-		err = io->data->callback->poll_revents(io->data, pfds, nfds, revents);
-		snd_pcm_lock(pcm);
+		if (snd_pcm_is_locked(pcm)) {
+			snd_pcm_unlock(pcm); /* to avoid deadlock */
+			err = io->data->callback->poll_revents(io->data, pfds, nfds, revents);
+			snd_pcm_lock(pcm);
+		} else {
+			err = io->data->callback->poll_revents(io->data, pfds, nfds, revents);
+		}
 	} else {
 		*revents = pfds->revents;
 		err = 0;
-- 
2.23.0

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  parent reply	other threads:[~2019-09-22  3:33 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-22  3:28 [alsa-devel] [PATCH 0/3] Make pcm_ioplug check lock status before locking (fixes pcm_jack lockups) Ben Russell
2019-09-22  3:28 ` [alsa-devel] [PATCH 1/3] pcm_local: Add snd_pcm_is_locked Ben Russell
2019-09-22  3:28 ` Ben Russell [this message]
2019-09-22  3:28 ` [alsa-devel] [PATCH 3/3] pcm_local: assert() when using mutexes incorrectly Ben Russell
2019-09-22 20:25 ` [alsa-devel] [PATCH 0/3] Make pcm_ioplug check lock status before locking (fixes pcm_jack lockups) Takashi Iwai
2019-09-24  7:45   ` Ben Russell
2019-09-24 10:18     ` Takashi Iwai
2019-09-25  6:10       ` Ben Russell

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