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exit: perform add_device_randomness() without tasklist_lock

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Parallel calls to add_device_randomness() contend on their own.

The clone side aleady runs outside of tasklist_lock, which in turn means
any caller on the exit side extends the tasklist_lock hold time while
contending on the random-private lock.

Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/r/20250206164415.450051-2-mjguzik@gmail.com
Acked-by: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Mateusz Guzik 2025-02-06 17:44:10 +01:00 • committed by Christian Brauner
commit 1ab2785694
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1 changed files with 2 additions and 3 deletions
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5
kernel/exit.c
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@ -174,9 +174,6 @@ static void __exit_signal(struct task_struct *tsk)
sig->curr_target = next_thread(tsk);
}
add_device_randomness((const void*) &tsk->se.sum_exec_runtime,
sizeof(unsigned long long));
/*
* Accumulate here the counters for all threads as they die. We could
* skip the group leader because it is the last user of signal_struct,
@ -270,6 +267,8 @@ repeat:
write_unlock_irq(&tasklist_lock);
proc_flush_pid(thread_pid);
put_pid(thread_pid);
add_device_randomness(&p->se.sum_exec_runtime,
sizeof(p->se.sum_exec_runtime));
release_thread(p);
/*
* This task was already removed from the process/thread/pid lists