[PATCH 5.4 1/2] Revert "btrfs: avoid monopolizing a core when activating a swap file"

[PATCH 5.4 1/2] Revert "btrfs: avoid monopolizing a core when activating a swap file"

[Koichiro Den]

This reverts commit 3d770d44dd5c6316913b003790998404636ec2a8.

The backport for linux-5.4.y, commit 3d770d44dd5c ("btrfs: avoid
monopolizing a core when activating a swap file"), inserted
cond_resched() in the wrong location.

Revert it now; a subsequent commit will re-backport the original patch.

Fixes: 3d770d44dd5c ("btrfs: avoid monopolizing a core when activating a swap file") # linux-5.4.y
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
---
 fs/btrfs/inode.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index d9a581f46f13..cd72409ccc94 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7679,8 +7679,6 @@ noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
 			ret = -EAGAIN;
 			goto out;
 		}
-
-		cond_resched();
 	}
 
 	btrfs_release_path(path);
-- 
2.45.2

[PATCH 5.4 2/2] btrfs: avoid monopolizing a core when activating a swap file

[Koichiro Den]

From: Filipe Manana <fdmanana@suse.com>

commit 2c8507c63f5498d4ee4af404a8e44ceae4345056 upstream.

This commit re-attempts the backport of the change to the linux-5.4.y
branch. Commit 3d770d44dd5c ("btrfs: avoid monopolizing a core when
activating a swap file") on this branch was reverted.

During swap activation we iterate over the extents of a file and we can
have many thousands of them, so we can end up in a busy loop monopolizing
a core. Avoid this by doing a voluntary reschedule after processing each
extent.

CC: stable@vger.kernel.org # 5.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
---
 fs/btrfs/inode.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index cd72409ccc94..004894e6dd23 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -11079,6 +11079,8 @@ static int btrfs_swap_activate(struct swap_info_struct *sis, struct file *file,
 		}
 
 		start += len;
+
+		cond_resched();
 	}
 
 	if (bsi.block_len)
-- 
2.45.2

Re: [PATCH 5.4 1/2] Revert "btrfs: avoid monopolizing a core when activating a swap file"

[Sasha Levin]

[ Sasha's backport helper bot ]

Hi,

No upstream commit was identified. Using temporary commit for testing.

Results of testing on various branches:

| Branch                    | Patch Apply | Build Test |
|---------------------------|-------------|------------|
| stable/linux-5.4.y        |  Success    |  Failed    |

Build Errors:
Build error for stable/linux-5.4.y:
    ssh: connect to host 192.168.1.58 port 22: No route to host