pidfs: ensure consistent ENOENT/ESRCH reporting
In a prior patch series we tried to cleanly differentiate between:
(1) The task has already been reaped.
(2) The caller requested a pidfd for a thread-group leader but the pid
actually references a struct pid that isn't used as a thread-group
leader.
as this was causing issues for non-threaded workloads.
But there's cases where the current simple logic is wrong. Specifically,
if the pid was a leader pid and the check races with __unhash_process().
Stabilize this by using a sequence counter associated with tasklist_lock
and retry while we're in __unhash_process(). The seqcounter might be
useful independent of pidfs.
Signed-off-by: Christian Brauner <brauner@kernel.org>
4 files changed
