When I added the ability for syncfs to report writeback errors, I
neglected to adequately protect file->f_sb_err. We could have racing
updates to that value if two tasks are issuing syncfs() on the same
fd at the same time.
Fix this by protecting the f_sb_err field with the file->f_lock,
similarly to how the f_wb_err field is protected.
Cc: stable@xxxxxxxxxxxxxxx # v5.8+
Fixes: 735e4ae5ba28 (vfs: track per-sb writeback errors and report them to syncfs)
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
---
fs/sync.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
I sent this a couple of weeks ago, but no one picked it up. No changes
from the original posting, but added the Fixes tag and marked it for
stable.
diff --git a/fs/sync.c b/fs/sync.c
index 1373a610dc78..3be26ff72431 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -162,7 +162,7 @@ SYSCALL_DEFINE1(syncfs, int, fd)
{
struct fd f = fdget(fd);
struct super_block *sb;
- int ret, ret2;
+ int ret, ret2 = 0;
if (!f.file)
return -EBADF;
@@ -172,7 +172,12 @@ SYSCALL_DEFINE1(syncfs, int, fd)
ret = sync_filesystem(sb);
up_read(&sb->s_umount);
- ret2 = errseq_check_and_advance(&sb->s_wb_err, &f.file->f_sb_err);
+ if (errseq_check(&sb->s_wb_err, f.file->f_sb_err)) {
+ /* Something changed, must use slow path */
+ spin_lock(&f.file->f_lock);
+ ret2 = errseq_check_and_advance(&sb->s_wb_err, &f.file->f_sb_err);
+ spin_unlock(&f.file->f_lock);
+ }
fdput(f);
return ret ? ret : ret2;
--
2.29.2
