linux-kernel - [PATCH v2 0/2] pidfs: ensure consistent ENOENT/ESRCH reporting

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Message-Id: <20250411-work-pidfs-enoent-v2-0-60b2d3bb545f@kernel.org>
Date: Fri, 11 Apr 2025 15:22:43 +0200
From: Christian Brauner <brauner@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: linux-fsdevel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>, 
 Lennart Poettering <lennart@...ttering.net>, 
 Daan De Meyer <daan.j.demeyer@...il.com>, Mike Yuan <me@...dnzj.com>, 
 linux-kernel@...r.kernel.org, Peter Ziljstra <peterz@...radead.org>, 
 Christian Brauner <brauner@...nel.org>
Subject: [PATCH v2 0/2] 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 the pidfd waitqueue lock.

Signed-off-by: Christian Brauner <brauner@...nel.org>
---
Christian Brauner (2):
      exit: move wake_up_all() pidfd waiters into __unhash_process()
      pidfs: ensure consistent ENOENT/ESRCH reporting

 kernel/exit.c |  5 +++++
 kernel/fork.c | 31 +++++++++++++------------------
 kernel/pid.c  |  5 -----
 3 files changed, 18 insertions(+), 23 deletions(-)
---
base-commit: 1e940fff94374d04b6c34f896ed9fbad3d2fb706
change-id: 20250411-work-pidfs-enoent-747579160c8c