[alsa-devel] [PATCH] ALSA: pcm: Fix starvation on down_write_nonblock()
Commit 67ec1072b053 (ALSA: pcm: Fix rwsem deadlock for non-atomic PCM stream) fixes deadlock for non-atomic PCM stream. But, This patch causes antother stuck. If writer is RT thread and reader is a normal thread, the reader thread will be difficult to get scheduled. It may not give chance to release read locks and writer gets stuck for a long time or forever if they are pinned to single cpu.
To fix this, The writer gives reader a chance to be scheduled by using the minimum msleep() instaed of spinning. This is for concept, We may need to change the function name and comments or suggest another approach.
Signed-off-by: Chanho Min chanho.min@lge.com --- sound/core/pcm_native.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 66c90f4..88d4aab 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -96,7 +96,7 @@ static DECLARE_RWSEM(snd_pcm_link_rwsem); static inline void down_write_nonblock(struct rw_semaphore *lock) { while (!down_write_trylock(lock)) - cond_resched(); + msleep(1); }
#define PCM_LOCK_DEFAULT 0
Hi Chanho,
I love your patch! Yet something to improve:
[auto build test ERROR on sound/for-next] [also build test ERROR on v4.20-rc3 next-20181123] [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Chanho-Min/ALSA-pcm-Fix-starvation-... base: https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git for-next config: x86_64-randconfig-x001-201846 (attached as .config) compiler: gcc-7 (Debian 7.3.0-1) 7.3.0 reproduce: # save the attached .config to linux build tree make ARCH=x86_64
All errors (new ones prefixed by >>):
sound/core/pcm_native.c: In function 'down_write_nonblock':
sound/core/pcm_native.c:99:3: error: implicit declaration of function 'msleep' [-Werror=implicit-function-declaration]
msleep(1); ^~~~~~ cc1: some warnings being treated as errors
vim +/msleep +99 sound/core/pcm_native.c
89 90 /* Writer in rwsem may block readers even during its waiting in queue, 91 * and this may lead to a deadlock when the code path takes read sem 92 * twice (e.g. one in snd_pcm_action_nonatomic() and another in 93 * snd_pcm_stream_lock()). As a (suboptimal) workaround, let writer to 94 * spin until it gets the lock. 95 */ 96 static inline void down_write_nonblock(struct rw_semaphore *lock) 97 { 98 while (!down_write_trylock(lock))
99 msleep(1);
100 } 101
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Hi Chanho,
I love your patch! Yet something to improve:
[auto build test ERROR on sound/for-next] [also build test ERROR on v4.20-rc3 next-20181123] [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Chanho-Min/ALSA-pcm-Fix-starvation-... base: https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git for-next config: x86_64-allmodconfig (attached as .config) compiler: gcc-7 (Debian 7.3.0-1) 7.3.0 reproduce: # save the attached .config to linux build tree make ARCH=x86_64
All errors (new ones prefixed by >>):
include/linux/slab.h:332:43: warning: dubious: x & !y include/linux/slab.h:332:43: warning: dubious: x & !y include/linux/slab.h:332:43: warning: dubious: x & !y include/linux/slab.h:332:43: warning: dubious: x & !y sound/core/pcm_native.c:590:51: warning: incorrect type in assignment (different base types) sound/core/pcm_native.c:590:51: expected restricted snd_pcm_state_t [usertype] state sound/core/pcm_native.c:590:51: got int [signed] state sound/core/pcm_native.c:755:38: warning: incorrect type in argument 2 (different base types) sound/core/pcm_native.c:755:38: expected int [signed] state sound/core/pcm_native.c:755:38: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:767:38: warning: incorrect type in argument 2 (different base types) sound/core/pcm_native.c:767:38: expected int [signed] state sound/core/pcm_native.c:767:38: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:816:38: warning: incorrect type in argument 2 (different base types) sound/core/pcm_native.c:816:38: expected int [signed] state sound/core/pcm_native.c:816:38: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1226:32: warning: incorrect type in assignment (different base types) sound/core/pcm_native.c:1226:32: expected restricted snd_pcm_state_t [usertype] state sound/core/pcm_native.c:1226:32: got int [signed] state sound/core/pcm_native.c:1250:31: warning: incorrect type in argument 3 (different base types) sound/core/pcm_native.c:1250:31: expected int [signed] state sound/core/pcm_native.c:1250:31: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1257:40: warning: incorrect type in argument 3 (different base types) sound/core/pcm_native.c:1257:40: expected int [signed] state sound/core/pcm_native.c:1257:40: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1283:28: warning: restricted snd_pcm_state_t degrades to integer sound/core/pcm_native.c:1285:40: warning: incorrect type in assignment (different base types) sound/core/pcm_native.c:1285:40: expected restricted snd_pcm_state_t [usertype] state sound/core/pcm_native.c:1285:40: got int [signed] state sound/core/pcm_native.c:1309:64: warning: incorrect type in argument 3 (different base types) sound/core/pcm_native.c:1309:64: expected int [signed] state sound/core/pcm_native.c:1309:64: got restricted snd_pcm_state_t [usertype] state sound/core/pcm_native.c:1325:38: warning: incorrect type in argument 3 (different base types) sound/core/pcm_native.c:1325:38: expected int [signed] state sound/core/pcm_native.c:1325:38: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1684:38: warning: incorrect type in argument 2 (different base types) sound/core/pcm_native.c:1684:38: expected int [signed] state sound/core/pcm_native.c:1684:38: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1750:61: warning: incorrect type in argument 2 (different base types) sound/core/pcm_native.c:1750:61: expected int [signed] state sound/core/pcm_native.c:1750:61: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1751:63: warning: incorrect type in argument 2 (different base types) sound/core/pcm_native.c:1751:63: expected int [signed] state sound/core/pcm_native.c:1751:63: got restricted snd_pcm_state_t [usertype] <noident> sound/core/pcm_native.c:1768:76: warning: incorrect type in initializer (different base types) sound/core/pcm_native.c:1768:76: expected int [signed] new_state sound/core/pcm_native.c:1768:76: got restricted snd_pcm_state_t include/linux/slab.h:332:43: warning: dubious: x & !y
sound/core/pcm_native.c:99:17: error: undefined identifier 'msleep' sound/core/pcm_native.c:99:23: error: not a function <noident>
sound/core/pcm_native.c:2089:26: warning: restricted snd_pcm_format_t degrades to integer sound/core/pcm_native.c:2093:54: warning: incorrect type in argument 1 (different base types) sound/core/pcm_native.c:2093:54: expected restricted snd_pcm_format_t [usertype] format sound/core/pcm_native.c:2093:54: got unsigned int [unsigned] [assigned] k sound/core/pcm_native.c:2111:26: warning: restricted snd_pcm_format_t degrades to integer sound/core/pcm_native.c:2115:54: warning: incorrect type in argument 1 (different base types) sound/core/pcm_native.c:2115:54: expected restricted snd_pcm_format_t [usertype] format sound/core/pcm_native.c:2115:54: got unsigned int [unsigned] [assigned] k sound/core/pcm_native.c:2295:30: warning: restricted snd_pcm_access_t degrades to integer sound/core/pcm_native.c:2297:30: warning: restricted snd_pcm_access_t degrades to integer sound/core/pcm_native.c:2300:38: warning: restricted snd_pcm_access_t degrades to integer sound/core/pcm_native.c:2302:38: warning: restricted snd_pcm_access_t degrades to integer sound/core/pcm_native.c:2304:38: warning: restricted snd_pcm_access_t degrades to integer sound/core/pcm_native.c:2314:86: warning: restricted snd_pcm_subformat_t degrades to integer include/linux/slab.h:332:43: warning: dubious: x & !y include/linux/slab.h:332:43: warning: dubious: x & !y include/linux/slab.h:332:43: warning: dubious: x & !y sound/core/pcm_compat.c:226:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:226:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:226:13: got restricted snd_pcm_state_t [addressable] [assigned] [usertype] state sound/core/pcm_compat.c:235:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:235:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:235:13: got restricted snd_pcm_state_t [addressable] [assigned] [usertype] suspended_state sound/core/pcm_compat.c:290:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:290:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:290:13: got restricted snd_pcm_state_t [addressable] [assigned] [usertype] state sound/core/pcm_compat.c:299:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:299:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:299:13: got restricted snd_pcm_state_t [addressable] [assigned] [usertype] suspended_state include/linux/slab.h:332:43: warning: dubious: x & !y include/linux/slab.h:332:43: warning: dubious: x & !y sound/core/pcm_compat.c:525:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:525:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:525:13: got restricted snd_pcm_state_t [assigned] [usertype] state sound/core/pcm_compat.c:528:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:528:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:528:13: got restricted snd_pcm_state_t [assigned] [usertype] suspended_state sound/core/pcm_compat.c:614:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:614:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:614:13: got restricted snd_pcm_state_t [assigned] [usertype] state sound/core/pcm_compat.c:617:13: warning: incorrect type in assignment (different base types) sound/core/pcm_compat.c:617:13: expected signed int [signed] [explicitly-signed] __pu_val sound/core/pcm_compat.c:617:13: got restricted snd_pcm_state_t [assigned] [usertype] suspended_state sound/core/pcm_native.c:127:9: warning: context imbalance in '__snd_pcm_stream_lock_mode' - different lock contexts for basic block sound/core/pcm_native.c:137:28: warning: context imbalance in '__snd_pcm_stream_unlock_mode' - unexpected unlock sound/core/pcm_native.c:1097:52: warning: context imbalance in 'snd_pcm_action_group' - unexpected unlock sound/core/pcm_native.c: In function 'down_write_nonblock': sound/core/pcm_native.c:99:3: error: implicit declaration of function 'msleep' [-Werror=implicit-function-declaration] msleep(1); ^~~~~~ cc1: some warnings being treated as errors
vim +/msleep +99 sound/core/pcm_native.c
89 90 /* Writer in rwsem may block readers even during its waiting in queue, 91 * and this may lead to a deadlock when the code path takes read sem 92 * twice (e.g. one in snd_pcm_action_nonatomic() and another in 93 * snd_pcm_stream_lock()). As a (suboptimal) workaround, let writer to 94 * spin until it gets the lock. 95 */ 96 static inline void down_write_nonblock(struct rw_semaphore *lock) 97 { 98 while (!down_write_trylock(lock))
99 msleep(1);
100 } 101
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