FAILED: patch "[PATCH] btrfs: do not zero f_bavail if we have available space" failed to apply to 4.9-stable tree

FAILED: patch "[PATCH] btrfs: do not zero f_bavail if we have available space" failed to apply to 4.9-stable tree

[gregkh]

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 d55966c4279bfc6a0cf0b32bf13f5df228a1eeb6 Mon Sep 17 00:00:00 2001
From: Josef Bacik <josef@toxicpanda.com>
Date: Fri, 31 Jan 2020 09:31:05 -0500
Subject: [PATCH] btrfs: do not zero f_bavail if we have available space

There was some logic added a while ago to clear out f_bavail in statfs()
if we did not have enough free metadata space to satisfy our global
reserve.  This was incorrect at the time, however didn't really pose a
problem for normal file systems because we would often allocate chunks
if we got this low on free metadata space, and thus wouldn't really hit
this case unless we were actually full.

Fast forward to today and now we are much better about not allocating
metadata chunks all of the time.  Couple this with d792b0f19711 ("btrfs:
always reserve our entire size for the global reserve") which now means
we'll easily have a larger global reserve than our free space, we are
now more likely to trip over this while still having plenty of space.

Fix this by skipping this logic if the global rsv's space_info is not
full.  space_info->full is 0 unless we've attempted to allocate a chunk
for that space_info and that has failed.  If this happens then the space
for the global reserve is definitely sacred and we need to report
b_avail == 0, but before then we can just use our calculated b_avail.

Reported-by: Martin Steigerwald <martin@lichtvoll.de>
Fixes: ca8a51b3a979 ("btrfs: statfs: report zero available if metadata are exhausted")
CC: stable@vger.kernel.org # 4.5+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Tested-By: Martin Steigerwald <martin@lichtvoll.de>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index a906315efd19..0616a5434793 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2135,7 +2135,15 @@ static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	 */
 	thresh = SZ_4M;
 
-	if (!mixed && total_free_meta - thresh < block_rsv->size)
+	/*
+	 * We only want to claim there's no available space if we can no longer
+	 * allocate chunks for our metadata profile and our global reserve will
+	 * not fit in the free metadata space.  If we aren't ->full then we
+	 * still can allocate chunks and thus are fine using the currently
+	 * calculated f_bavail.
+	 */
+	if (!mixed && block_rsv->space_info->full &&
+	    total_free_meta - thresh < block_rsv->size)
 		buf->f_bavail = 0;
 
 	buf->f_type = BTRFS_SUPER_MAGIC;