Another deadlock on HEAD #2704
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Not really, this is a production OpenVZ node with 92 containers with very volatile load - as it's a container hosting, I don't have reach into the CTs. But it has deadlocked after 2hrs of uptime and then after some 8hrs again. |
behlendorf
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Dec 19, 2014
It is known that mutexes in Linux are not safe when using them to synchronize the freeing of object in which the mutex is embedded: http://lwn.net/Articles/575477/ The known places in ZFS which are suspected to suffer from the race condition are zio->io_lock and dbuf->db_mtx. * zio uses zio->io_lock and zio->io_cv to synchronize freeing between zio_wait() and zio_done(). * dbuf uses dbuf->db_mtx to protect reference counting. This patch fixes this kind of race by forcing serialization on mutex_exit() with a spin lock, making the mutex safe by sacrificing a bit of performance and memory overhead. This issue most commonly manifests itself as a deadlock in the zio pipeline caused by a process spinning on the damaged mutex. Similar deadlocks have been reported for the dbuf->db_mtx mutex. And it can also cause a NULL dereference or bad paging request under the right circumstances. This issue any many like it are linked off the openzfs/zfs#2523 issue. Specifically this fix resolves at least the following outstanding issues: openzfs/zfs#401 openzfs/zfs#2523 openzfs/zfs#2679 openzfs/zfs#2684 openzfs/zfs#2704 openzfs/zfs#2708 openzfs/zfs#2517 openzfs/zfs#2827 openzfs/zfs#2850 openzfs/zfs#2891 openzfs/zfs#2897 openzfs/zfs#2247 openzfs/zfs#2939 Signed-off-by: Chunwei Chen <tuxoko@gmail.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Richard Yao <ryao@gentoo.org> Closes #421
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This issue which is a duplicate of #2523 was resolved by the following commit. Full details can be found in the commit message and related lwn article. openzfs/spl@a3c1eb7 mutex: force serialization on mutex_exit() to fix races |
dajhorn
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Dec 20, 2014
Commit: openzfs/zfs@a3c1eb7 From: Chunwei Chen <tuxoko@gmail.com> Date: Fri, 19 Dec 2014 11:31:59 +0800 Subject: mutex: force serialization on mutex_exit() to fix races It is known that mutexes in Linux are not safe when using them to synchronize the freeing of object in which the mutex is embedded: http://lwn.net/Articles/575477/ The known places in ZFS which are suspected to suffer from the race condition are zio->io_lock and dbuf->db_mtx. * zio uses zio->io_lock and zio->io_cv to synchronize freeing between zio_wait() and zio_done(). * dbuf uses dbuf->db_mtx to protect reference counting. This patch fixes this kind of race by forcing serialization on mutex_exit() with a spin lock, making the mutex safe by sacrificing a bit of performance and memory overhead. This issue most commonly manifests itself as a deadlock in the zio pipeline caused by a process spinning on the damaged mutex. Similar deadlocks have been reported for the dbuf->db_mtx mutex. And it can also cause a NULL dereference or bad paging request under the right circumstances. This issue any many like it are linked off the openzfs/zfs#2523 issue. Specifically this fix resolves at least the following outstanding issues: openzfs/zfs#401 openzfs/zfs#2523 openzfs/zfs#2679 openzfs/zfs#2684 openzfs/zfs#2704 openzfs/zfs#2708 openzfs/zfs#2517 openzfs/zfs#2827 openzfs/zfs#2850 openzfs/zfs#2891 openzfs/zfs#2897 openzfs/zfs#2247 openzfs/zfs#2939 Signed-off-by: Chunwei Chen <tuxoko@gmail.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Richard Yao <ryao@gentoo.org> Backported-by: Darik Horn <dajhorn@vanadac.com> Closes #421 Conflicts: include/sys/mutex.h
behlendorf
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Dec 23, 2014
It is known that mutexes in Linux are not safe when using them to synchronize the freeing of object in which the mutex is embedded: http://lwn.net/Articles/575477/ The known places in ZFS which are suspected to suffer from the race condition are zio->io_lock and dbuf->db_mtx. * zio uses zio->io_lock and zio->io_cv to synchronize freeing between zio_wait() and zio_done(). * dbuf uses dbuf->db_mtx to protect reference counting. This patch fixes this kind of race by forcing serialization on mutex_exit() with a spin lock, making the mutex safe by sacrificing a bit of performance and memory overhead. This issue most commonly manifests itself as a deadlock in the zio pipeline caused by a process spinning on the damaged mutex. Similar deadlocks have been reported for the dbuf->db_mtx mutex. And it can also cause a NULL dereference or bad paging request under the right circumstances. This issue any many like it are linked off the openzfs/zfs#2523 issue. Specifically this fix resolves at least the following outstanding issues: openzfs/zfs#401 openzfs/zfs#2523 openzfs/zfs#2679 openzfs/zfs#2684 openzfs/zfs#2704 openzfs/zfs#2708 openzfs/zfs#2517 openzfs/zfs#2827 openzfs/zfs#2850 openzfs/zfs#2891 openzfs/zfs#2897 openzfs/zfs#2247 openzfs/zfs#2939 Signed-off-by: Chunwei Chen <tuxoko@gmail.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Richard Yao <ryao@gentoo.org> Closes #421
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@behlendorf This is not a duplicate of #2523. Instead, it is a duplicate of #3091, provided that this deadlock occurred on a multi-socket system. |
Closed
ryao
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Feb 19, 2015
It is known that mutexes in Linux are not safe when using them to synchronize the freeing of object in which the mutex is embedded: http://lwn.net/Articles/575477/ The known places in ZFS which are suspected to suffer from the race condition are zio->io_lock and dbuf->db_mtx. * zio uses zio->io_lock and zio->io_cv to synchronize freeing between zio_wait() and zio_done(). * dbuf uses dbuf->db_mtx to protect reference counting. This patch fixes this kind of race by forcing serialization on mutex_exit() with a spin lock, making the mutex safe by sacrificing a bit of performance and memory overhead. This issue most commonly manifests itself as a deadlock in the zio pipeline caused by a process spinning on the damaged mutex. Similar deadlocks have been reported for the dbuf->db_mtx mutex. And it can also cause a NULL dereference or bad paging request under the right circumstances. This issue any many like it are linked off the openzfs/zfs#2523 issue. Specifically this fix resolves at least the following outstanding issues: openzfs/zfs#401 openzfs/zfs#2523 openzfs/zfs#2679 openzfs/zfs#2684 openzfs/zfs#2704 openzfs/zfs#2708 openzfs/zfs#2517 openzfs/zfs#2827 openzfs/zfs#2850 openzfs/zfs#2891 openzfs/zfs#2897 openzfs/zfs#2247 openzfs/zfs#2939 Signed-off-by: Chunwei Chen <tuxoko@gmail.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Richard Yao <ryao@gentoo.org> Closes openzfs#421 Conflicts: include/sys/mutex.h
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Hi,
one of my machines keeps locking down with ZFS on current HEAD, Linux: 2.6.32-042stab093.4 (OpenVZ kernel).
process stacks:
https://gist.github.com/snajpa/3761bde377aeef8de77f
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