This is a note to let you know that I've just added the patch titled
Btrfs: check if previous transaction aborted to avoid fs corruption
to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-check-if-previous-transaction-aborted-to-avoid-fs-corruption.patch
and it can be found in the queue-4.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From 1f9b8c8fbc9a4d029760b16f477b9d15500e3a34 Mon Sep 17 00:00:00 2001
From: Filipe Manana <[email protected]>
Date: Wed, 12 Aug 2015 11:54:35 +0100
Subject: Btrfs: check if previous transaction aborted to avoid fs corruption
From: Filipe Manana <[email protected]>
commit 1f9b8c8fbc9a4d029760b16f477b9d15500e3a34 upstream.
While we are committing a transaction, it's possible the previous one is
still finishing its commit and therefore we wait for it to finish first.
However we were not checking if that previous transaction ended up getting
aborted after we waited for it to commit, so we ended up committing the
current transaction which can lead to fs corruption because the new
superblock can point to trees that have had one or more nodes/leafs that
were never durably persisted.
The following sequence diagram exemplifies how this is possible:
CPU 0 CPU 1
transaction N starts
(...)
btrfs_commit_transaction(N)
cur_trans->state = TRANS_STATE_COMMIT_START;
(...)
cur_trans->state = TRANS_STATE_COMMIT_DOING;
(...)
cur_trans->state = TRANS_STATE_UNBLOCKED;
root->fs_info->running_transaction = NULL;
btrfs_start_transaction()
--> starts
transaction N + 1
btrfs_write_and_wait_transaction(trans, root);
--> starts writing all new or COWed ebs created
at transaction N
creates some new
ebs, COWs some
existing ebs but
doesn't COW or
deletes eb X
btrfs_commit_transaction(N + 1)
(...)
cur_trans->state = TRANS_STATE_COMMIT_START;
(...)
wait_for_commit(root, prev_trans);
-->
prev_trans == transaction N
btrfs_write_and_wait_transaction() continues
writing ebs
--> fails writing eb X, we abort transaction N
and set bit BTRFS_FS_STATE_ERROR on
fs_info->fs_state, so no new transactions
can start after setting that bit
cleanup_transaction()
btrfs_cleanup_one_transaction()
wakes up task at CPU 1
continues,
doesn't abort because
cur_trans->aborted (transaction N + 1)
is zero, and no
checks for bit
BTRFS_FS_STATE_ERROR in fs_info->fs_state
are made
btrfs_write_and_wait_transaction(trans, root);
--> succeeds,
no errors during writeback
write_ctree_super(trans, root, 0);
--> succeeds
--> we have
now a superblock that points us
to some
root that uses eb X, which was
never
written to disk
In this scenario future attempts to read eb X from disk results in an
error message like "parent transid verify failed on X wanted Y found Z".
So fix this by aborting the current transaction if after waiting for the
previous transaction we verify that it was aborted.
Signed-off-by: Filipe Manana <[email protected]>
Reviewed-by: Josef Bacik <[email protected]>
Reviewed-by: Liu Bo <[email protected]>
Signed-off-by: Chris Mason <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
fs/btrfs/transaction.c | 3 +++
1 file changed, 3 insertions(+)
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -1875,8 +1875,11 @@ int btrfs_commit_transaction(struct btrf
spin_unlock(&root->fs_info->trans_lock);
wait_for_commit(root, prev_trans);
+ ret = prev_trans->aborted;
btrfs_put_transaction(prev_trans);
+ if (ret)
+ goto cleanup_transaction;
} else {
spin_unlock(&root->fs_info->trans_lock);
}
Patches currently in stable-queue which might be from [email protected] are
queue-4.1/btrfs-check-if-previous-transaction-aborted-to-avoid-fs-corruption.patch
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