Commit 39f17c70 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Andrew Morton
Browse files

sched/task.h: fix the wrong comment on task_lock() nesting with tasklist_lock 

The ancient comment above task_lock() states that it can be nested outside
of read_lock(&tasklist_lock), but this is no longer true:

  CPU_0			CPU_1			CPU_2

  task_lock()		read_lock(tasklist)
  						write_lock_irq(tasklist)
  read_lock(tasklist)	task_lock()

Unless CPU_0 calls read_lock() in IRQ context, queued_read_lock_slowpath()
won't get the lock immediately, it will spin waiting for the pending
writer on CPU_2, resulting in a deadlock.

Link: https://lkml.kernel.org/r/20250914110908.GA18769@redhat.com


Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent f23e76a3

include/linux/sched/task.h

+2 −3
Original line number Diff line number Diff line
@@ -210,9 +210,8 @@ static inline struct vm_struct *task_stack_vm_area(const struct task_struct *t) 
 * pins the final release of task.io_context.  Also protects ->cpuset and

 * ->cgroup.subsys[]. And ->vfork_done. And ->sysvshm.shm_clist.

 *

 * Nests both inside and outside of read_lock(&tasklist_lock).

 * It must not be nested with write_lock_irq(&tasklist_lock),

 * neither inside nor outside.

 * Nests inside of read_lock(&tasklist_lock). It must not be nested with

 * write_lock_irq(&tasklist_lock), neither inside nor outside.

 */

static inline void task_lock(struct task_struct *p)

{