The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ba0b084ac309283db6e329785c1dc4f45fdbd379 Mon Sep 17 00:00:00 2001

From: Filipe Manana fdmanana@suse.com Date: Wed, 16 Oct 2019 16:28:52 +0100 Subject: [PATCH] Btrfs: check for the full sync flag while holding the inode lock during fsync

We were checking for the full fsync flag in the inode before locking the inode, which is racy, since at that that time it might not be set but after we acquire the inode lock some other task set it. One case where this can happen is on a system low on memory and some concurrent task failed to allocate an extent map and therefore set the full sync flag on the inode, to force the next fsync to work in full mode.

A consequence of missing the full fsync flag set is hitting the problems fixed by commit 0c713cbab620 ("Btrfs: fix race between ranged fsync and writeback of adjacent ranges"), BUG_ON() when dropping extents from a log tree, hitting assertion failures at tree-log.c:copy_items() or all sorts of weird inconsistencies after replaying a log due to file extents items representing ranges that overlap.

So just move the check such that it's done after locking the inode and before starting writeback again.

Fixes: 0c713cbab620 ("Btrfs: fix race between ranged fsync and writeback of adjacent ranges") CC: stable@vger.kernel.org # 5.2+ Signed-off-by: Filipe Manana fdmanana@suse.com Signed-off-by: David Sterba dsterba@suse.com

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c index e955e7fa9201..435a502a3226 100644 --- a/fs/btrfs/file.c +++ b/fs/btrfs/file.c @@ -2067,25 +2067,7 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync) struct btrfs_trans_handle *trans; struct btrfs_log_ctx ctx; int ret = 0, err; - u64 len;

- /* - * If the inode needs a full sync, make sure we use a full range to - * avoid log tree corruption, due to hole detection racing with ordered - * extent completion for adjacent ranges, and assertion failures during - * hole detection. - */ - if (test_bit(BTRFS_INODE_NEEDS_FULL_SYNC, - &BTRFS_I(inode)->runtime_flags)) { - start = 0; - end = LLONG_MAX; - } - - /* - * The range length can be represented by u64, we have to do the typecasts - * to avoid signed overflow if it's [0, LLONG_MAX] eg. from fsync() - */ - len = (u64)end - (u64)start + 1; trace_btrfs_sync_file(file, datasync);

btrfs_init_log_ctx(&ctx, inode); @@ -2111,6 +2093,19 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)

atomic_inc(&root->log_batch);

+ /* + * If the inode needs a full sync, make sure we use a full range to + * avoid log tree corruption, due to hole detection racing with ordered + * extent completion for adjacent ranges, and assertion failures during + * hole detection. Do this while holding the inode lock, to avoid races + * with other tasks. + */ + if (test_bit(BTRFS_INODE_NEEDS_FULL_SYNC, + &BTRFS_I(inode)->runtime_flags)) { + start = 0; + end = LLONG_MAX; + } + /* * Before we acquired the inode's lock, someone may have dirtied more * pages in the target range. We need to make sure that writeback for @@ -2138,8 +2133,11 @@ int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync) /* * We have to do this here to avoid the priority inversion of waiting on * IO of a lower priority task while holding a transaction open. + * + * Also, the range length can be represented by u64, we have to do the + * typecasts to avoid signed overflow if it's [0, LLONG_MAX]. */ - ret = btrfs_wait_ordered_range(inode, start, len); + ret = btrfs_wait_ordered_range(inode, start, (u64)end - (u64)start + 1); if (ret) { up_write(&BTRFS_I(inode)->dio_sem); inode_unlock(inode);