Fix Change Details
------------------
(Compare with comment #3)
The xattr dir/child inodes are evicted/disposed
immediately on file removal, not on shrinker.
$ touch /zfs/file
<...>-23940 [006] d... 10808.746798: p_zfs_mknode_0:
(zfs_mknode+0x0/0xe00 [zfs]) flag=0x0 dzp=0xffff88011aa94400
<...>-23940 [006] d... 10808.746925: p_zfs_znode_alloc_0:
(zfs_znode_alloc+0x0/0x520 [zfs]) obj=0xa
<...>-23940 [006] d... 10808.746938: r_zfs_znode_alloc_0:
(zfs_mknode+0x8a3/0xe00 [zfs] <- zfs_znode_alloc) zpp=0xffff88011aa90880
$ setfattr -n user.debug -v 1 /zfs/file
<...>-23941 [006] d... 10818.945733: p_zfs_mknode_0:
(zfs_mknode+0x0/0xe00 [zfs]) flag=0x2 dzp=0xffff88011aa90880
<...>-23941 [006] d... 10818.945892: p_zfs_znode_alloc_0:
(zfs_znode_alloc+0x0/0x520 [zfs]) obj=0xb
<...>-23941 [006] d... 10818.945905: r_zfs_znode_alloc_0:
(zfs_mknode+0x8a3/0xe00 [zfs] <- zfs_znode_alloc) zpp=0xffff88011aa961c0
<...>-23941 [006] d... 10818.945925: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xa
setfattr-23941 [006] d... 10818.945929: r_zfs_zget_0:
(zfs_zaccess+0x12b/0x220 [zfs] <- zfs_zget)
setfattr-23941 [006] d... 10818.945933: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xa
setfattr-23941 [006] d... 10818.945936: r_zfs_zget_0:
(zfs_zaccess+0x12b/0x220 [zfs] <- zfs_zget)
setfattr-23941 [006] d... 10818.945948: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xa
setfattr-23941 [006] d... 10818.945951: r_zfs_zget_0:
(zfs_zaccess+0x12b/0x220 [zfs] <- zfs_zget)
setfattr-23941 [006] d... 10818.945966: p_zfs_mknode_0:
(zfs_mknode+0x0/0xe00 [zfs]) flag=0x0 dzp=0xffff88011aa961c0
setfattr-23941 [006] d... 10818.945990: p_zfs_znode_alloc_0:
(zfs_znode_alloc+0x0/0x520 [zfs]) obj=0xc
setfattr-23941 [006] d... 10818.945996: r_zfs_znode_alloc_0:
(zfs_mknode+0x8a3/0xe00 [zfs] <- zfs_znode_alloc) zpp=0xffff88011aa90440
$ rm /zfs/file
<...>-23942 [006] d... 10822.453456: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xa
<...>-23942 [006] d... 10822.453469: r_zfs_zget_0:
(zfs_dirent_lock+0x56c/0x6c0 [zfs] <- zfs_zget)
rm-23942 [006] d... 10822.453494: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xb
rm-23942 [006] d... 10822.453498: r_zfs_zget_0:
(zfs_remove+0x22b/0x4c0 [zfs] <- zfs_zget)
rm-23942 [006] d... 10822.453597: p_zpl_evict_inode_0:
(zpl_evict_inode+0x0/0x60 [zfs]) inode=0xffff88011aa90a90
rm-23942 [006] d... 10822.453602: p_zfs_inactive_0:
(zfs_inactive+0x0/0x270 [zfs]) inode=0xffff88011aa90a90
rm-23942 [006] d... 10822.453603: p_zfs_zinactive_0:
(zfs_zinactive+0x0/0xe0 [zfs]) znode=0xffff88011aa90880 obj=0xa
rm-23942 [006] d... 10822.453607: p_zfs_rmnode_0:
(zfs_rmnode+0x0/0x360 [zfs]) znode=0xffff88011aa90880
rm-23942 [006] d... 10822.453619: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xb
rm-23942 [006] d... 10822.453623: r_zfs_zget_0:
(zfs_rmnode+0x25b/0x360 [zfs] <- zfs_zget)
rm-23942 [006] d... 10822.453656: p_zfs_iput_async_0:
(zfs_iput_async+0x0/0x60 [zfs]) inode=0xffff88011aa963d0 obj=0x0
z_iput-23904 [006] d... 10822.453675: p_zpl_evict_inode_0:
(zpl_evict_inode+0x0/0x60 [zfs]) inode=0xffff88011aa963d0
z_iput-23904 [006] d... 10822.453676: p_zfs_inactive_0:
(zfs_inactive+0x0/0x270 [zfs]) inode=0xffff88011aa963d0
z_iput-23904 [006] d... 10822.453677: p_zfs_zinactive_0:
(zfs_zinactive+0x0/0xe0 [zfs]) znode=0xffff88011aa961c0 obj=0xb
z_iput-23904 [006] d... 10822.453679: p_zfs_rmnode_0:
(zfs_rmnode+0x0/0x360 [zfs]) znode=0xffff88011aa961c0
z_iput-23904 [006] d... 10822.453681: p_zfs_purgedir_0:
(zfs_purgedir+0x0/0x230 [zfs]) znode=0xffff88011aa961c0
z_iput-23904 [006] d... 10822.453686: p_zfs_zget_0:
(zfs_zget+0x0/0x230 [zfs]) zsb=0xffff880016f00000 obj=0xc
z_iput-23904 [006] d... 10822.453690: r_zfs_zget_0:
(zfs_purgedir+0xb4/0x230 [zfs] <- zfs_zget)
z_iput-23904 [006] d... 10822.453713: p_zfs_iput_async_0:
(zfs_iput_async+0x0/0x60 [zfs]) inode=0xffff88011aa90650 obj=0x0
z_iput-23904 [006] d... 10822.453719: r_zfs_purgedir_0:
(zfs_rmnode+0x272/0x360 [zfs] <- zfs_purgedir)
z_iput-23904 [006] d... 10822.453755: p_zpl_evict_inode_0:
(zpl_evict_inode+0x0/0x60 [zfs]) inode=0xffff88011aa90650
z_iput-23904 [006] d... 10822.453756: p_zfs_inactive_0:
(zfs_inactive+0x0/0x270 [zfs]) inode=0xffff88011aa90650
z_iput-23904 [006] d... 10822.453757: p_zfs_zinactive_0:
(zfs_zinactive+0x0/0xe0 [zfs]) znode=0xffff88011aa90440 obj=0xc
z_iput-23904 [006] d... 10822.453759: p_zfs_rmnode_0:
(zfs_rmnode+0x0/0x360 [zfs]) znode=0xffff88011aa90440
$ echo 2 | sudo tee /proc/sys/vm/drop_caches
2
<...>-23945 [005] d... 10836.555639: p_dispose_list_0:
(dispose_list+0x0/0x50)
<...>-23945 [005] d... 10836.555775: p_dispose_list_0:
(dispose_list+0x0/0x50)
<...>-23945 [005] d... 10836.560865: p_dispose_list_0:
(dispose_list+0x0/0x50)
<...>-23945 [005] d... 10836.560993: p_dispose_list_0:
(dispose_list+0x0/0x50)
<...>-23945 [005] d... 10836.567297: p_dispose_list_0:
(dispose_list+0x0/0x50)
<...>-23945 [005] d... 10836.567371: p_dispose_list_0:
(dispose_list+0x0/0x50)
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https://bugs.launchpad.net/bugs/1839521
Title:
Xenial: ZFS deadlock in shrinker path with xattrs
Status in zfs-linux package in Ubuntu:
Invalid
Status in zfs-linux source package in Xenial:
In Progress
Status in zfs-linux source package in Bionic:
Invalid
Status in zfs-linux source package in Disco:
Invalid
Status in zfs-linux source package in Eoan:
Invalid
Bug description:
[Impact]
* Xenial's ZFS can deadlock in the memory shrinker path
after removing files with extended attributes (xattr).
* Extended attributes are enabled by default, but are
_not_ used by default, which reduces the likelyhood.
* It's very difficult/rare to reproduce this problem,
due to file/xattr/remove/shrinker/lru order/timing
circumstances required. (weeks for a reporter user)
but a synthetic test-case has been found for tests.
[Test Case]
* A synthetic reproducer is available for this LP,
with a few steps to touch/setfattr/rm/drop_caches
plus a kernel module to massage the disposal list.
* In the original ZFS module:
the xattr dir inode is not purged immediately on
file removal, but possibly purged _two_ shrinker
invocations later. This allows for other thread
started before file remove to call zfs_zget() on
the xattr child inode and iput() it, so it makes
to the same disposal list as the xattr dir inode.
* In the modified ZFS module:
the xattr dir inode is purged immediately on file
removal not possibly later on shrinker invocation,
so the problem window above doesn't exist anymore.
[Regression Potential]
* Low. The patches are confined to extended attributes
in ZFS, specifically node removal/purge, and another
change how an xattr child inode tracks its xattr dir
(parent) inode, so that it can be purged immediately
on removal.
* The ZFS test-suite has been run on original/modified
zfs-dkms package/kernel modules, with no regressions.
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https://bugs.launchpad.net/ubuntu/+source/zfs-linux/+bug/1839521/+subscriptions
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