Ping?
On 2020/08/19 21:42, Tetsuo Handa wrote:
> __fput_sync() was introduced by commit 4a9d4b024a3102fc ("switch fput to
> task_work_add") with BUG_ON(!(current->flags & PF_KTHREAD)) check, and
> the only user of __fput_sync() was introduced by commit 17c0a5aaffa63da6
> ("make acct_kill() wait for file closing."). However, the latter commit is
> effectively calling __fput_sync() from !PF_KTHREAD thread because of
> schedule_work() call followed by immediate wait_for_completion() call.
> That is, there is no need to defer close_work() to a WQ context. I guess
> that the reason to defer was nothing but to bypass this BUG_ON() check.
> While we need to remain careful about calling __fput_sync(), we can remove
> bypassable BUG_ON() check from __fput_sync().
>
> If this change is accepted, racy fput()+flush_delayed_fput() introduced
> by commit e2dc9bf3f5275ca3 ("umd: Transform fork_usermode_blob into
> fork_usermode_driver") will be replaced by this raceless __fput_sync().
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> ---
> fs/file_table.c | 15 +++++----------
> 1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/fs/file_table.c b/fs/file_table.c
> index 656647f..7c41251 100644
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -359,20 +359,15 @@ void fput(struct file *file)
> }
>
> /*
> - * synchronous analog of fput(); for kernel threads that might be needed
> - * in some umount() (and thus can't use flush_delayed_fput() without
> - * risking deadlocks), need to wait for completion of __fput() and know
> - * for this specific struct file it won't involve anything that would
> - * need them. Use only if you really need it - at the very least,
> - * don't blindly convert fput() by kernel thread to that.
> + * synchronous analog of fput(); for threads that need to wait for completion
> + * of __fput() and know for this specific struct file it won't involve anything
> + * that would need them. Use only if you really need it - at the very least,
> + * don't blindly convert fput() to __fput_sync().
> */
> void __fput_sync(struct file *file)
> {
> - if (atomic_long_dec_and_test(&file->f_count)) {
> - struct task_struct *task = current;
> - BUG_ON(!(task->flags & PF_KTHREAD));
> + if (atomic_long_dec_and_test(&file->f_count))
> __fput(file);
> - }
> }
>
> EXPORT_SYMBOL(fput);
>
