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Always wait for txg sync when umounting dataset

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Currently, when unmounting a filesystem, ZFS will only wait for
a txg sync if the dataset is dirty and not readonly. However, this
can be problematic in cases where a dataset is remounted readonly
immediately before being unmounted, which often happens when the
system is being shut down. Since encrypted datasets require that
all I/O is completed before the dataset is disowned, this issue
causes problems when write I/Os leak into the txgs after the
dataset is disowned, which can happen when sync=disabled.

While looking into fixes for this issue, it was discovered that
dsl_dataset_is_dirty() does not return B_TRUE when the dataset has
been removed from the txg dirty datasets list, but has not actually
been processed yet. Furthermore, the implementation is comletely
different from dmu_objset_is_dirty(), adding to the confusion.
Rather than relying on this function, this patch forces the umount
code path (and the remount readonly code path) to always perform a
txg sync on read-write datasets and removes the function altogether.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tom Caputi <tcaputi@datto.com>
Closes #7753
Closes #7795
This commit is contained in:
Tom Caputi
2018-08-20 16:42:17 -04:00
committed by Brian Behlendorf
parent 8c4fb36a24
commit 47ab01a18f
5 changed files with 26 additions and 33 deletions
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module/zfs/zfs_vfsops.c
+6 -3
View File
@@ -1745,10 +1745,10 @@ zfsvfs_teardown(zfsvfs_t *zfsvfs, boolean_t unmounting)
zfs_unregister_callbacks(zfsvfs);
/*
* Evict cached data
* Evict cached data. We must write out any dirty data before
* disowning the dataset.
*/
if (dsl_dataset_is_dirty(dmu_objset_ds(zfsvfs->z_os)) &&
!zfs_is_readonly(zfsvfs))
if (!zfs_is_readonly(zfsvfs))
txg_wait_synced(dmu_objset_pool(zfsvfs->z_os), 0);
dmu_objset_evict_dbufs(zfsvfs->z_os);
@@ -1970,6 +1970,9 @@ zfs_remount(struct super_block *sb, int *flags, zfs_mnt_t *zm)
if (error)
return (error);
if (!zfs_is_readonly(zfsvfs) && (*flags & MS_RDONLY))
txg_wait_synced(dmu_objset_pool(zfsvfs->z_os), 0);
zfs_unregister_callbacks(zfsvfs);
zfsvfs_vfs_free(zfsvfs->z_vfs);