Re: [RFC PATCH] fuse: permit freezing while waiting for request answer

[Miklos Szeredi]

On Wed, 12 Aug 2026 at 11:54, Sergey Senozhatsky
<senozhatsky@xxxxxxxxxxxx> wrote:
>
> Suspend freezes tasks in random order and doesn't take into
> consideration producer-consumer dependency that may exist
> between tasks.  One example where this can cause issues is:
> fuse server getting frozen ahead of clients, which then get
> stuck waiting for req answers that never come (the server
> is already frozen):
>
>  PM: suspend entry (s2idle)
>  Filesystems sync: 0.018 seconds
>  Freezing user space processes
>  Freezing user space processes failed after 20.001 seconds (1 tasks refusing to freeze, wq_busy=0):
>  task:ThreadPoolForeg state:D stack:0     pid:7873  tgid:7854  ppid:7827   flags:0x00004006
>  Call Trace:
>   <TASK>
>   __schedule+0x554/0x1320
>   ? vprintk_emit+0x2a8/0x320
>   schedule+0x5e/0xd0
>   __fuse_simple_request+0x4c8/0x6d0
>   fuse_do_getattr+0x1e9/0x320
>   fuse_update_get_attr+0x362/0x6a0
>   fuse_file_read_iter+0x13a/0x1b0
>   vfs_read+0x29f/0x2f0
>   ksys_read+0x75/0xf0
>   do_syscall_64+0x70/0xf0
>
> Make all wait-event calls in request_wait_answer() freezer-friendly.
> This uses TASK_FREEZABLE_UNSAFE because often time we freeze holding
> locks (in the upper layers), which triggers debug_locks warning.

If the lock is uncontended, then fine.  If something's waiting on such
a lock, then the freezing will still fail.  This is unfortunate, but
still better than failing the uncontended case as well.  So I don't
see an issue with this.

Thanks,
Miklos