[PATCH 0/2] btrfs: fixes for nowait buffered writes

[PATCH 0/2] btrfs: fixes for nowait buffered writes

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

A couple fixes for the recently added support for nowait buffered writes.
Trivial stuff, one of the bugs was reported sometime ago by the lkp test
robot.

Filipe Manana (2):
  btrfs: fix nowait buffered write returning -ENOSPC
  btrfs: fix inode reserve space leak due to nowait buffered write

 fs/btrfs/file.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

-- 
2.35.1

[PATCH 1/2] btrfs: fix nowait buffered write returning -ENOSPC

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

If we are doing a buffered write in NOWAIT context and we can't reserve
metadata space due to -ENOSPC, then we should return -EAGAIN so that we
retry the write in a context allowed to block and do metadata reservation
with flushing, which might succeed this time due to the allowed flushing.

Returning -ENOSPC while in NOWAIT context simply makes some writes fail
with -ENOSPC when they would likely succeed after switching from NOWAIT
context to blocking context. That is unexpected behaviour and even fio
complains about it with a warning like this:

  fio: io_u error on file /mnt/sdi/task_0.0.0: No space left on device: write offset=1535705088, buflen=65536
  fio: pid=592630, err=28/file:io_u.c:1846, func=io_u error, error=No space left on device

The fio's job config is this:

   [global]
   bs=64K
   ioengine=io_uring
   iodepth=1
   size=2236962133
   nr_files=1
   filesize=2236962133
   direct=0
   runtime=10
   fallocate=posix
   io_size=2236962133
   group_reporting
   time_based

   [task_0]
   rw=randwrite
   directory=/mnt/sdi
   numjobs=4

So fix this by returning -EAGAIN if we are in NOWAIT context and the
metadata reservation failed with -ENOSPC.

Fixes: 304e45acdb8f ("btrfs: plumb NOWAIT through the write path")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index b7855f794ba6..75d4d0bc9d8f 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1286,6 +1286,9 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
 						write_bytes);
 			else
 				btrfs_check_nocow_unlock(BTRFS_I(inode));
+
+			if (nowait && ret == -ENOSPC)
+				ret = -EAGAIN;
 			break;
 		}
 
-- 
2.35.1

[PATCH 2/2] btrfs: fix inode reserve space leak due to nowait buffered write

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

During a nowait buffered write, if we fail to balance dirty pages we exit
btrfs_buffered_write() without releasing the delalloc space reserved for
an extent, resulting in leaking space from the inode's block reserve.

So fix that by releasing the delalloc space for the extent when balancing
dirty pages fails.

Reported-by: kernel test robot <yujie.liu@intel.com>
Link: https://lore.kernel.org/all/202210111304.d369bc32-yujie.liu@intel.com
Fixes: 965f47aeb5de ("btrfs: make btrfs_buffered_write nowait compatible")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/file.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 75d4d0bc9d8f..f8be9d629e75 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1295,8 +1295,10 @@ static noinline ssize_t btrfs_buffered_write(struct kiocb *iocb,
 		release_bytes = reserve_bytes;
 again:
 		ret = balance_dirty_pages_ratelimited_flags(inode->i_mapping, bdp_flags);
-		if (ret)
+		if (ret) {
+			btrfs_delalloc_release_extents(BTRFS_I(inode), reserve_bytes);
 			break;
+		}
 
 		/*
 		 * This is going to setup the pages array with the number of
-- 
2.35.1

Re: [PATCH 0/2] btrfs: fixes for nowait buffered writes

[Josef Bacik]

On Wed, Nov 02, 2022 at 12:46:34PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> A couple fixes for the recently added support for nowait buffered writes.
> Trivial stuff, one of the bugs was reported sometime ago by the lkp test
> robot.
> 
> Filipe Manana (2):
>   btrfs: fix nowait buffered write returning -ENOSPC
>   btrfs: fix inode reserve space leak due to nowait buffered write
> 
>  fs/btrfs/file.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef 

Re: [PATCH 0/2] btrfs: fixes for nowait buffered writes

[David Sterba]

On Wed, Nov 02, 2022 at 12:46:34PM +0000, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> A couple fixes for the recently added support for nowait buffered writes.
> Trivial stuff, one of the bugs was reported sometime ago by the lkp test
> robot.
> 
> Filipe Manana (2):
>   btrfs: fix nowait buffered write returning -ENOSPC
>   btrfs: fix inode reserve space leak due to nowait buffered write

Added to misc-next, thanks.