At the moment we can not reliably and deterministically test that the
transaction abortion code works as expected. For example in the past [1]
we had an issue where that code returned the pinned extents to the free
space caches allowing fstrim to perform a discard against the physical
locations of the extents, and worse, when the fs was mounted with the
option -o discard it explicitly did a discard on each pinned extent.
This resulted in filesystem corruption, leaving the fs unmountable.
This patch adds a debugfs file named abort_transaction, which has a
default value of 0, can only be written by someone with root privileges
and when a non-zero value is written to it, it makes all subsequent
transaction commits fail at the very end (right before writing the new
superblock), which results in a transaction abortion.
This way we can for example write a deterministic fstest for commit [1]
which looks like:
_supported_fs btrfs
_supported_os Linux
_require_scratch
_require_btrfs_debugfs "abort_transaction"
_need_to_be_root
rm -f $seqres.full
# We will abort a btrfs transaction later, which always produces a warning in
# dmesg. We do not want the test to fail because of this.
_disable_dmesg_check
_scratch_mkfs >>$seqres.full 2>&1
_scratch_mount "-o discard"
_require_batched_discard $SCRATCH_MNT
# Create a file and commit the current transaction.
echo -n "hello" > $SCRATCH_MNT/foo
sync
# Now update the file, which forces a COW operation of the fs root, adding
# the old root location to the pinned extents list.
echo -n " world" >> $SCRATCH_MNT/foo
# Now abort the current transaction, unmount the fs, mount it again and verify
# we can open the file and read its content (which should match what it had
# when the last transaction committed successfully). Btrfs used to issue a
# discard operation on the extents in the pinned extents list, resulting in
# corruption of metadata and data, and used too to return the pinned extents
# to the free space caches, allowing future fstrim operations to perform a
# discard operation against the pinned exents.
echo 1 > $BTRFS_DEBUG_FS/abort_transaction
sync
echo 0 > $BTRFS_DEBUG_FS/abort_transaction
$FSTRIM_PROG $SCRATCH_MNT
_scratch_unmount
_scratch_mount
echo "File content after transaction abort + remount: $(cat $SCRATCH_MNT/foo)"
The test's expected output is:
File content after transaction abort + remount: hello
With patch [1] reverted the test fails with:
btrfs/088 2s ... - output mismatch (see /home/fdmanana/git/hub/xfstests/results//btrfs/088.out.bad)
--- tests/btrfs/088.out 2015-03-31 19:31:17.558436298 +0100
+++ /home/fdmanana/git/hub/xfstests/results//btrfs/088.out.bad 2015-03-31 19:58:12.741403640 +0100
@@ -1,2 +1,8 @@
QA output created by 088
-File content after transaction abort + remount: hello
+mount: wrong fs type, bad option, bad superblock on /dev/sdc,
+ missing codepage or helper program, or other error
+ In some cases useful info is found in syslog - try
+ dmesg | tail or so
+
...
(Run 'diff -u tests/btrfs/088.out /home/fdmanana/git/hub/xfstests/results//btrfs/088.out.bad' to see the entire diff)
_check_btrfs_filesystem: filesystem on /dev/sdc is inconsistent (see /home/fdmanana/git/hub/xfstests/results//btrfs/088.full)
$ cat /home/fdmanana/git/hub/xfstests/results//btrfs/088.full
(...)
_check_btrfs_filesystem: filesystem on /dev/sdc is inconsistent
*** fsck.btrfs output ***
Check tree block failed, want=29573120, have=0
Check tree block failed, want=29573120, have=0
Check tree block failed, want=29573120, have=0
Check tree block failed, want=29573120, have=0
Check tree block failed, want=29573120, have=0
read block failed check_tree_block
Couldn't read tree root
Couldn't open file system
*** end fsck.btrfs output
[1] commit 678886bdc637 ("Btrfs: fix fs corruption on transaction abort
if device supports discard")
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
---
If there are no objections to the feature/interface, I will submit a test
for fstests.
fs/btrfs/sysfs.c | 11 +++++++++++
fs/btrfs/sysfs.h | 2 ++
fs/btrfs/transaction.c | 9 +++++++++
3 files changed, 22 insertions(+)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index 94edb0a..4b10f3b 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -666,6 +666,7 @@ static struct dentry *btrfs_debugfs_root_dentry;
/* Debugging tunables and exported data */
u64 btrfs_debugfs_test;
+static u32 btrfs_debugfs_abort_transaction;
int btrfs_sysfs_add_one(struct btrfs_fs_info *fs_info)
{
@@ -719,10 +720,20 @@ static int btrfs_init_debugfs(void)
debugfs_create_u64("test", S_IRUGO | S_IWUGO, btrfs_debugfs_root_dentry,
&btrfs_debugfs_test);
+
+ debugfs_create_bool("abort_transaction",
+ S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH,
+ btrfs_debugfs_root_dentry,
+ &btrfs_debugfs_abort_transaction);
#endif
return 0;
}
+bool debugfs_abort_transaction(void)
+{
+ return btrfs_debugfs_abort_transaction != 0;
+}
+
int btrfs_init_sysfs(void)
{
int ret;
diff --git a/fs/btrfs/sysfs.h b/fs/btrfs/sysfs.h
index f7dd298..517dbb3 100644
--- a/fs/btrfs/sysfs.h
+++ b/fs/btrfs/sysfs.h
@@ -74,4 +74,6 @@ int btrfs_kobj_add_device(struct btrfs_fs_info *fs_info,
struct btrfs_device *one_device);
int btrfs_kobj_rm_device(struct btrfs_fs_info *fs_info,
struct btrfs_device *one_device);
+
+bool debugfs_abort_transaction(void);
#endif /* _BTRFS_SYSFS_H_ */
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 5d8cff8..f514ff9 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -32,6 +32,7 @@
#include "volumes.h"
#include "dev-replace.h"
#include "qgroup.h"
+#include "sysfs.h"
#define BTRFS_ROOT_TRANS_TAG 0
@@ -2029,6 +2030,14 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans,
goto scrub_continue;
}
+ if (unlikely(debugfs_abort_transaction())) {
+ btrfs_warn(root->fs_info,
+ "Aborting transaction due to debugfs request.");
+ mutex_unlock(&root->fs_info->tree_log_mutex);
+ ret = -EIO;
+ goto scrub_continue;
+ }
+
ret = write_ctree_super(trans, root, 0);
if (ret) {
mutex_unlock(&root->fs_info->tree_log_mutex);
--
2.1.3
--
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