This is a note to let you know that I've just added the patch titled
btrfs: properly enable async discard when switching from RO->RW
to the 6.3-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-properly-enable-async-discard-when-switching-from-ro-rw.patch
and it can be found in the queue-6.3 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 981a37bab5e5f16137266d3f00cf2bd018af36ef Mon Sep 17 00:00:00 2001
From: Chris Mason <clm@xxxxxx>
Date: Mon, 5 Jun 2023 12:03:15 -0700
Subject: btrfs: properly enable async discard when switching from RO->RW
From: Chris Mason <clm@xxxxxx>
commit 981a37bab5e5f16137266d3f00cf2bd018af36ef upstream.
The async discard uses the BTRFS_FS_DISCARD_RUNNING bit in the fs_info
to force discards off when the filesystem has aborted or we're generally
not able to run discards. This gets flipped on when we're mounted rw,
and also when we go from ro->rw.
Commit 63a7cb13071842 ("btrfs: auto enable discard=async when possible")
enabled async discard by default, and this meant
"mount -o ro /dev/xxx /yyy" had async discards turned on.
Unfortunately, this meant our check in btrfs_remount_cleanup() would see
that discards are already on:
/* If we toggled discard async */
if (!btrfs_raw_test_opt(old_opts, DISCARD_ASYNC) &&
btrfs_test_opt(fs_info, DISCARD_ASYNC))
btrfs_discard_resume(fs_info);
So, we'd never call btrfs_discard_resume() when remounting the root
filesystem from ro->rw.
drgn shows this really nicely:
import os
import sys
from drgn.helpers.linux.fs import path_lookup
from drgn import NULL, Object, Type, cast
def btrfs_sb(sb):
return cast("struct btrfs_fs_info *", sb.s_fs_info)
if len(sys.argv) == 1:
path = "/"
else:
path = sys.argv[1]
fs_info = cast("struct btrfs_fs_info *", path_lookup(prog, path).mnt.mnt_sb.s_fs_info)
BTRFS_FS_DISCARD_RUNNING = 1 << prog['BTRFS_FS_DISCARD_RUNNING']
if fs_info.flags & BTRFS_FS_DISCARD_RUNNING:
print("discard running flag is on")
else:
print("discard running flag is off")
[root]# mount | grep nvme
/dev/nvme0n1p3 on / type btrfs
(rw,relatime,compress-force=zstd:3,ssd,discard=async,space_cache=v2,subvolid=5,subvol=/)
[root]# ./discard_running.drgn
discard running flag is off
[root]# mount -o remount,discard=sync /
[root]# mount -o remount,discard=async /
[root]# ./discard_running.drgn
discard running flag is on
The fix is to call btrfs_discard_resume() when we're going from ro->rw.
It already checks to make sure the async discard flag is on, so it'll do
the right thing.
Fixes: 63a7cb13071842 ("btrfs: auto enable discard=async when possible")
CC: stable@xxxxxxxxxxxxxxx # 6.3+
Reviewed-by: Boris Burkov <boris@xxxxxx>
Signed-off-by: Chris Mason <clm@xxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/btrfs/super.c | 6 ++++++
1 file changed, 6 insertions(+)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1840,6 +1840,12 @@ static int btrfs_remount(struct super_bl
btrfs_clear_sb_rdonly(sb);
set_bit(BTRFS_FS_OPEN, &fs_info->flags);
+
+ /*
+ * If we've gone from readonly -> read/write, we need to get
+ * our sync/async discard lists in the right state.
+ */
+ btrfs_discard_resume(fs_info);
}
out:
/*
Patches currently in stable-queue which might be from clm@xxxxxx are
queue-6.3/btrfs-properly-enable-async-discard-when-switching-from-ro-rw.patch
queue-6.3/btrfs-can_nocow_file_extent-should-pass-down-args-strict-from-callers.patch
