Commit 1df4bd83 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Andrew Morton
Browse files

do_io_accounting: use sig->stats_lock 

Rather than lock_task_sighand(), sig->stats_lock was specifically designed
for this type of use.

This way the "if (whole)" branch runs lockless in the likely case.

Link: https://lkml.kernel.org/r/20231023153405.GA4639@redhat.com


Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 23202220

fs/proc/base.c

+14 −6
Original line number Diff line number Diff line
@@ -2973,7 +2973,6 @@ static const struct file_operations proc_coredump_filter_operations = { 
static int do_io_accounting(struct task_struct *task, struct seq_file *m, int whole)

{

	struct task_io_accounting acct;

	unsigned long flags;

	int result;



	result = down_read_killable(&task->signal->exec_update_lock);
@@ -2985,15 +2984,24 @@ static int do_io_accounting(struct task_struct *task, struct seq_file *m, int wh 
		goto out_unlock;

	}



	if (whole && lock_task_sighand(task, &flags)) {

	if (whole) {

		struct signal_struct *sig = task->signal;

		struct task_struct *t;

		unsigned int seq = 1;

		unsigned long flags;



		rcu_read_lock();

		do {

			seq++; /* 2 on the 1st/lockless path, otherwise odd */

			flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);



			acct = sig->ioac;

			__for_each_thread(sig, t)

				task_io_accounting_add(&acct, &t->ioac);



		unlock_task_sighand(task, &flags);

		} while (need_seqretry(&sig->stats_lock, seq));

		done_seqretry_irqrestore(&sig->stats_lock, seq, flags);

		rcu_read_unlock();

	} else {

		acct = task->ioac;

	}