Dear all I noticed the bug while setting up a backup with fsfreeze and restic. How I reproduce it: 1. Write multiple MB to a file (eg. 100MB) while after one or two MB freeze the filesystem from the sidecar pod 2. From the sidecar pod, issue multiple `strace tail /generated/data/0.txt` 3. After a couple of tries strace shows that the `read(...)` works but `close(...)` hangs 4. From now on all `read(...)` operations are blocked until the freeze is lifted System: Ubuntu 18.04.3 LTS CPU: Intel(R) Xeon(R) CPU X5650 @ 2.67GHz Storage: /dev/mapper/mpathXX on /var/lib/kubelet/plugins/hpe.com/... type xfs (rw,noatime,attr2,inode64,noquota) I used this tool to generate the file. The number of concurrent files does not appear to matter that much. I was able to trigger the bug, tested with 2, 4 and 32 parallel files: https://gitlab.com/dns2utf8/multi_file_writer Cheers, Stefan PS: I opened a bug at the tool vendor too: https://github.com/vmware-tanzu/velero/issues/2113
On Wed, Dec 11, 2019 at 02:03:52PM +0000, bugzilla-daemon@bugzilla.kernel.org wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=205833 > > Bug ID: 205833 > Summary: fsfreeze blocks close(fd) on xfs sometimes > Product: File System > Version: 2.5 > Kernel Version: 4.15.0-55-generic #60-Ubuntu > Hardware: Intel > OS: Linux > Tree: Mainline > Status: NEW > Severity: normal > Priority: P1 > Component: XFS > Assignee: filesystem_xfs@kernel-bugs.kernel.org > Reporter: kernel.org@estada.ch > Regression: No > > Dear all > > I noticed the bug while setting up a backup with fsfreeze and restic. > > How I reproduce it: > > 1. Write multiple MB to a file (eg. 100MB) while after one or two MB > freeze > the filesystem from the sidecar pod > 2. From the sidecar pod, issue multiple `strace tail > /generated/data/0.txt` > 3. After a couple of tries strace shows that the `read(...)` works but > `close(...)` hangs > 4. From now on all `read(...)` operations are blocked until the freeze is > lifted > I'm not familiar with your user environment, but it sounds like the use case is essentially to read a file concurrently being written to and freeze the fs. From there, you're expecting the readers to exit but instead observe them blocked on close(). The ceaveat to note here is that close() is not necessarily a read-only operation from the perspective of XFS internals. A close() (or ->release() from the fs perspective) can do things like truncate post-eof block allocation, which requires a transaction and thus blocks on a frozen fs. To confirm, could you post a stack trace of one of your blocked reader tasks (i.e. 'cat /proc/<pid>/stack')? I'm not necessarily sure blocking here is a bug if that is the situation. We most likely wouldn't want to skip post-eof truncation on a file simply because the fs was frozen. That said, I thought Dave had proposed patches at one point to mitigate free space fragmentation side effects of post-eof truncation, and one such patch was to skip the truncation on read-only fds. I'll have to dig around or perhaps Dave can chime in, but I'm curious if that would also help with this use case.. Brian > System: Ubuntu 18.04.3 LTS > CPU: Intel(R) Xeon(R) CPU X5650 @ 2.67GHz > Storage: /dev/mapper/mpathXX on /var/lib/kubelet/plugins/hpe.com/... type xfs > (rw,noatime,attr2,inode64,noquota) > > I used this tool to generate the file. The number of concurrent files does > not > appear to matter that much. I was able to trigger the bug, tested with 2, 4 > and > 32 parallel files: > https://gitlab.com/dns2utf8/multi_file_writer > > Cheers, > Stefan > > PS: I opened a bug at the tool vendor too: > https://github.com/vmware-tanzu/velero/issues/2113 > > -- > You are receiving this mail because: > You are watching the assignee of the bug. >
Hi Brian Thank you! Here is the stack of a blocked `tail 0.txt` process: cat /proc/276/stack [<0>] call_rwsem_down_read_failed+0x18/0x30 [<0>] __percpu_down_read+0x58/0x80 [<0>] __sb_start_write+0x65/0x70 [<0>] xfs_trans_alloc+0xec/0x130 [xfs] [<0>] xfs_free_eofblocks+0x12a/0x1e0 [xfs] [<0>] xfs_release+0x144/0x170 [xfs] [<0>] xfs_file_release+0x15/0x20 [xfs] [<0>] __fput+0xea/0x220 [<0>] ____fput+0xe/0x10 [<0>] task_work_run+0x9d/0xc0 [<0>] ptrace_notify+0x84/0x90 [<0>] tracehook_report_syscall_exit+0x90/0xd0 [<0>] syscall_slow_exit_work+0x50/0xd0 [<0>] do_syscall_64+0x12b/0x130 [<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2 [<0>] 0xffffffffffffffff Your explanation matches the behaviour I see on the system. If there was a patch, do you think it would get backported or just stay in mainline and ship with the regular releases? Best, Stefan
On Tue, Dec 17, 2019 at 09:34:34AM +0000, bugzilla-daemon@bugzilla.kernel.org wrote: > https://bugzilla.kernel.org/show_bug.cgi?id=205833 > > --- Comment #2 from Stefan @dns2utf8 Schindler (kernel.org@estada.ch) --- > Hi Brian > > Thank you! Here is the stack of a blocked `tail 0.txt` process: > > cat /proc/276/stack > [<0>] call_rwsem_down_read_failed+0x18/0x30 > [<0>] __percpu_down_read+0x58/0x80 > [<0>] __sb_start_write+0x65/0x70 > [<0>] xfs_trans_alloc+0xec/0x130 [xfs] > [<0>] xfs_free_eofblocks+0x12a/0x1e0 [xfs] > [<0>] xfs_release+0x144/0x170 [xfs] > [<0>] xfs_file_release+0x15/0x20 [xfs] > [<0>] __fput+0xea/0x220 > [<0>] ____fput+0xe/0x10 > [<0>] task_work_run+0x9d/0xc0 > [<0>] ptrace_notify+0x84/0x90 > [<0>] tracehook_report_syscall_exit+0x90/0xd0 > [<0>] syscall_slow_exit_work+0x50/0xd0 > [<0>] do_syscall_64+0x12b/0x130 > [<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2 > [<0>] 0xffffffffffffffff > > Your explanation matches the behaviour I see on the system. > > If there was a patch, do you think it would get backported or just stay in > mainline and ship with the regular releases? > There was a patch, but it was RFC and hadn't been merged because IIRC more investigation/testing was required to evaluate side effects. For reference, the last post I see is the one below. In particular, patch 3 bypasses EOF block truncation from read-only file descriptors (I believe the file writer task would still block). https://marc.info/?l=linux-xfs&m=154951612101291&w=2 Based on the stack above, note that this is (at least for the time being) expected behavior on XFS. Brian > Best, > Stefan > > -- > You are receiving this mail because: > You are watching the assignee of the bug. >
Has the fix been merged? On the latest Arch Linux I am no longer able to reproduce the error where the second process hangs. My test files & programs are here: * Quick test: https://gitlab.com/dns2utf8/xfs_fsfreeze_test/ * Heavy load: https://gitlab.com/dns2utf8/multi_file_writer/ Best, Stefan
https://bugzilla.redhat.com/show_bug.cgi?id=1474726 the same bug