[PATCH 2/5] quota: make quotactl_fd(2) killable on s_umount

[Josef Bacik]

quotactl_fd(2) takes s_umount of the filesystem the file descriptor is on,
exclusively to turn quota on or off and shared for everything else.  If
the lock is held for a long time, by a syncfs(2) on a device which doesn't
answer say, the caller sits in D state and can't be killed.  For the
commands which write it does so holding write access to the mount.

quotactl(2) with a device can already be killed at this point, it gets the
lock from user_get_super().

All that has been done by the time the lock is taken is getting that write
access.  Use the killable variants, and drop it on the way out.

Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 fs/quota/quota.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/quota/quota.c b/fs/quota/quota.c
index f906e4fd3f0f..94e6407734c7 100644
--- a/fs/quota/quota.c
+++ b/fs/quota/quota.c
@@ -997,9 +997,11 @@ SYSCALL_DEFINE4(quotactl_fd, unsigned int, fd, unsigned int, cmd,
 
 	sb = fd_file(f)->f_path.mnt->mnt_sb;
 	if (quotactl_cmd_onoff(cmds))
-		down_write(&sb->s_umount);
+		ret = down_write_killable(&sb->s_umount);
 	else
-		down_read(&sb->s_umount);
+		ret = down_read_killable(&sb->s_umount);
+	if (ret)
+		goto out;
 
 	ret = do_quotactl(sb, type, cmds, id, addr, ERR_PTR(-EINVAL));
 
@@ -1007,7 +1009,7 @@ SYSCALL_DEFINE4(quotactl_fd, unsigned int, fd, unsigned int, cmd,
 		up_write(&sb->s_umount);
 	else
 		up_read(&sb->s_umount);
-
+out:
 	if (quotactl_cmd_write(cmds))
 		mnt_drop_write(fd_file(f)->f_path.mnt);
 	return ret;

-- 
2.55.0