Verified for Bionic, through the ZFS test suite. No new regressions were
reported, and results of the test suite are the same as for the previous
version.
ubuntu@z-rotomvm28:/usr/share/zfs$ dpkg -l |grep zfs-dkms
ii zfs-dkms 0.7.5-1ubuntu16.11
all OpenZFS filesystem kernel modules for Linux
** Tags added: verification-done-bionic
--
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to zfs-linux in Ubuntu.
https://bugs.launchpad.net/bugs/1916486
Title:
zfs_zrele_async can cause txg sync deadlocks
Status in zfs-linux package in Ubuntu:
Fix Released
Status in zfs-linux source package in Xenial:
Fix Committed
Status in zfs-linux source package in Bionic:
Fix Committed
Status in zfs-linux source package in Focal:
Fix Committed
Status in zfs-linux source package in Groovy:
Fix Committed
Status in zfs-linux source package in Hirsute:
Fix Released
Status in zfs-linux package in Debian:
New
Bug description:
[Impact]
TXG sync stalls, causing ZFS workloads to hang indefinitely
[Description]
For certain ZFS workloads, we can see hung task timeouts in the kernel logs
due to a transaction group deadlock. Userspace process will hang and display
stack traces similar to the one below:
[49181.619711] clnt_server D 0 21699 28868 0x00000320
[49181.619715] Call Trace:
[49181.619725] __schedule+0x24e/0x880
[49181.619730] schedule+0x2c/0x80
[49181.619750] cv_wait_common+0x11e/0x140 [spl]
[49181.619763] ? wait_woken+0x80/0x80
[49181.619775] __cv_wait+0x15/0x20 [spl]
[49181.619872] zil_commit.part.14+0x80/0x8c0 [zfs]
[49181.619884] ? _cond_resched+0x19/0x40
[49181.619887] ? mutex_lock+0x12/0x40
[49181.619959] zil_commit+0x17/0x20 [zfs]
[49181.620026] zfs_fsync+0x77/0xe0 [zfs]
[49181.620093] zpl_fsync+0x68/0xa0 [zfs]
[49181.620100] vfs_fsync_range+0x51/0xb0
[49181.620105] do_fsync+0x3d/0x70
[49181.620109] SyS_fsync+0x10/0x20
[49181.620114] do_syscall_64+0x73/0x130
[49181.620119] entry_SYSCALL_64_after_hwframe+0x41/0xa6
We also might see a kworker thread blocking in the zfs writeback/evict path:
[49181.881570] kworker/u17:3 D 0 4915 2 0x80000000
[49181.881576] Workqueue: writeback wb_workfn (flush-zfs-10)
[49181.881577] Call Trace:
[49181.881580] __schedule+0x24e/0x880
[49181.881582] ? atomic_t_wait+0x60/0x60
[49181.881584] schedule+0x2c/0x80
[49181.881588] bit_wait+0x11/0x60
[49181.881592] __wait_on_bit+0x4c/0x90
[49181.881596] ? atomic_t_wait+0x60/0x60
[49181.881599] __inode_wait_for_writeback+0xb9/0xf0
[49181.881601] ? bit_waitqueue+0x40/0x40
[49181.881605] inode_wait_for_writeback+0x26/0x40
[49181.881609] evict+0xb5/0x1a0
[49181.881611] iput+0x19c/0x230
[49181.881648] zfs_iput_async+0x1d/0x80 [zfs]
[49181.881682] zfs_get_data+0x1d4/0x2a0 [zfs]
[49181.881718] zil_commit.part.14+0x640/0x8c0 [zfs]
[49181.881752] zil_commit+0x17/0x20 [zfs]
[49181.881784] zpl_writepages+0xd5/0x160 [zfs]
[49181.881787] do_writepages+0x4b/0xe0
[49181.881790] __writeback_single_inode+0x45/0x350
[49181.881792] ? __writeback_single_inode+0x45/0x350
[49181.881794] writeback_sb_inodes+0x1d7/0x530
[49181.881796] wb_writeback+0xfb/0x300
[49181.881799] wb_workfn+0xad/0x400
[49181.881800] ? wb_workfn+0xad/0x400
[49181.881803] ? __switch_to_asm+0x35/0x70
[49181.881809] process_one_work+0x1de/0x420
[49181.881811] worker_thread+0x32/0x410
[49181.881813] kthread+0x121/0x140
[49181.881815] ? process_one_work+0x420/0x420
[49181.881817] ? kthread_create_worker_on_cpu+0x70/0x70
[49181.881819] ret_from_fork+0x35/0x40
This is caused by a race between ZFS writeback and evict threads,
usually during a transaction group sync operation. It's possible to
have two iput() threads racing for the same inode: one of them
scheduled async and the other executed synchronously as part of the
writeback path. If the writeback thread tries to evict the inode while
the async thread is running, it might re-enter the block layer for the
same inode due to ZFS counters being in an inconsistent state. This
then causes the kworker thread to stall the writeback, which in turn
prevents the transaction group sync to complete and locks other ZFS
threads.
This is fixed by the upstream commit:
- Fix zrele race in zrele_async that can cause hang (43eaef6de817) [0]
[Test Case]
Being a race condition, this issue has been hard to reproduce consistently.
This has been reported on heavy I/O workloads, mixing file creation and
deletion. We have some reports both from upstream and from Ubuntu users that
this is usually reproducible on e.g. heavy SQL workloads or on complex
ccache-enabled builds [1].
[0] https://github.com/openzfs/zfs/pull/11530
[1] https://github.com/openzfs/zfs/issues/11527
[Regression Potential]
The patch has been tested in the ZFS test suite and in production
environments, so the potential for further regressions should be fairly
controlled. Potential regressions might arise in the ZFS writeback path,
causing write hangs and eventually stalling all ZFS-backed operations
indefinitely. We should monitor heavy I/O workloads that put a lot of stress in
the sync and evict paths to exercise the new changes.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1916486/+subscriptions
--
Mailing list: https://launchpad.net/~kernel-packages
Post to : [email protected]
Unsubscribe : https://launchpad.net/~kernel-packages
More help : https://help.launchpad.net/ListHelp
