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fuse: use READ_ONCE in fuse_chan_num_background()

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fuse_chan_num_background() is called without holding fch->bg_lock (for
example from fuse_writepages() to compare against fc->congestion_threshold),
while fch->num_background is updated under bg_lock in dev.c and dev_uring.c.
This is the same locked-write/lockless-read pattern already used for
max_background in fuse_chan_max_background().

Use READ_ONCE() on the read side so that:

- The compiler does not cache or coalesce loads of a value that may change
  concurrently on another CPU.
- Prevent KCSAN from reporting an unexpected race.

Signed-off-by: Li Wang <liwang@kylinos.cn>
Fixes: 670d21c6e1 ("fuse: remove reliance on bdi congestion")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Li Wang 2026-05-22 16:38:05 +08:00 committed by Miklos Szeredi
parent a9489fbda7
commit 521fed4886
1 changed files with 1 additions and 1 deletions
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2
fs/fuse/dev.c
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@ -383,7 +383,7 @@ EXPORT_SYMBOL_GPL(fuse_dev_chan_new);
unsigned int fuse_chan_num_background(struct fuse_chan *fch)
{
return fch->num_background;
return READ_ONCE(fch->num_background);
}
unsigned int fuse_chan_max_background(struct fuse_chan *fch)