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| author | FAN YE <fy15309206903@gmail.com> | 2026-08-21 17:50:09 +0000 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2026-09-02 22:19:30 +0200 |
| commit | 2acb9f3d1cc8f65dc81ed55e238cbf8e5b60bff7 (patch) | |
| tree | eb33fed5b79264e854ed71a127d8fb3783a10bc1 /fs | |
| parent | cacf35832292997018837e484283f95a9301ebf5 (diff) | |
| download | linux-2acb9f3d1cc8f65dc81ed55e238cbf8e5b60bff7.tar.gz linux-2acb9f3d1cc8f65dc81ed55e238cbf8e5b60bff7.zip | |
btrfs: zstd: fix lost wakeup when waiting for a workspace
A writer can sleep forever in zstd_get_workspace() even though a workspace
is free. When zstd_alloc_workspace() fails, the task is queued on
zwsm->wait and schedules unconditionally, never re-testing the pool.
zstd_put_workspace() publishes the workspace and then calls cond_wake_up(),
which only wakes when a sleeper is already visible, so a workspace returned
between the failed allocation and prepare_to_wait() wakes nobody. The
window is wide: zstd_alloc_workspace() goes through kvmalloc() and may
enter reclaim.
Only a max level workspace triggers the wakeup and one is deliberately kept
allocated as the fallback every waiter waits for, so once its wakeup is
lost the writer stays in TASK_UNINTERRUPTIBLE until some other task happens
to return one. Re-check the pool after prepare_to_wait() has published the
waiter, and use the workspace if one turned up.
Fixes: 3f93aef535c8 ("btrfs: add zstd compression level support")
Assisted-by: Claude:claude-opus-5
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: FAN YE <fy15309206903@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/zstd.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/fs/btrfs/zstd.c b/fs/btrfs/zstd.c index 86919293fd54..58d9ff76fe07 100644 --- a/fs/btrfs/zstd.c +++ b/fs/btrfs/zstd.c @@ -307,8 +307,17 @@ again: DEFINE_WAIT(wait); prepare_to_wait(&zwsm->wait, &wait, TASK_UNINTERRUPTIBLE); - schedule(); + /* + * Re-check after being queued: zstd_put_workspace() only wakes + * a queue that already has a sleeper, so a workspace returned + * since the failed allocation woke nobody. + */ + ws = zstd_find_workspace(fs_info, level); + if (!ws) + schedule(); finish_wait(&zwsm->wait, &wait); + if (ws) + return ws; goto again; } |