From: Filipe Manana fdmanana@suse.com
[ Upstream commit 6b225baababf1e3d41a4250e802cbd193e1343fb ]
When we get an error flushing one device, during a super block commit, we record the error in the device structure, in the field 'last_flush_error'. This is used to later check if we should error out the super block commit, depending on whether the number of flush errors is greater than or equals to the maximum tolerated device failures for a raid profile.
However if we get a transient device flush error, unmount the filesystem and later try to mount it, we can fail the mount because we treat that past error as critical and consider the device is missing. Even if it's very likely that the error will happen again, as it's probably due to a hardware related problem, there may be cases where the error might not happen again. One example is during testing, and a test case like the new generic/648 from fstests always triggers this. The test cases generic/019 and generic/475 also trigger this scenario, but very sporadically.
When this happens we get an error like this:
$ mount /dev/sdc /mnt mount: /mnt wrong fs type, bad option, bad superblock on /dev/sdc, missing codepage or helper program, or other error.
$ dmesg (...) [12918.886926] BTRFS warning (device sdc): chunk 13631488 missing 1 devices, max tolerance is 0 for writable mount [12918.888293] BTRFS warning (device sdc): writable mount is not allowed due to too many missing devices [12918.890853] BTRFS error (device sdc): open_ctree failed
The failure happens because when btrfs_check_rw_degradable() is called at mount time, or at remount from RO to RW time, is sees a non zero value in a device's ->last_flush_error attribute, and therefore considers that the device is 'missing'.
Fix this by setting a device's ->last_flush_error to zero when we close a device, making sure the error is not seen on the next mount attempt. We only need to track flush errors during the current mount, so that we never commit a super block if such errors happened.
Signed-off-by: Filipe Manana fdmanana@suse.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/volumes.c | 13 +++++++++++++ 1 file changed, 13 insertions(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 509811aabb3f..bd4f0581c7c3 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -1147,6 +1147,19 @@ static void btrfs_close_one_device(struct btrfs_device *device) atomic_set(&device->dev_stats_ccnt, 0); extent_io_tree_release(&device->alloc_state);
+ /* + * Reset the flush error record. We might have a transient flush error + * in this mount, and if so we aborted the current transaction and set + * the fs to an error state, guaranteeing no super blocks can be further + * committed. However that error might be transient and if we unmount the + * filesystem and mount it again, we should allow the mount to succeed + * (btrfs_check_rw_degradable() should not fail) - if after mounting the + * filesystem again we still get flush errors, then we will again abort + * any transaction and set the error state, guaranteeing no commits of + * unsafe super blocks. + */ + device->last_flush_error = 0; + /* Verify the device is back in a pristine state */ ASSERT(!test_bit(BTRFS_DEV_STATE_FLUSH_SENT, &device->dev_state)); ASSERT(!test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));