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do_io_accounting: use sig->stats_lock

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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: Oleg Nesterov <oleg@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Oleg Nesterov 2023-10-23 17:34:05 +02:00 committed by Andrew Morton
parent 2320222067
commit 1df4bd83cd
1 changed files with 14 additions and 6 deletions
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20
fs/proc/base.c
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@ -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;
acct = sig->ioac;
__for_each_thread(sig, t)
task_io_accounting_add(&acct, &t->ioac);
rcu_read_lock();
do {
seq++; /* 2 on the 1st/lockless path, otherwise odd */
flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq);
unlock_task_sighand(task, &flags);
acct = sig->ioac;
__for_each_thread(sig, t)
task_io_accounting_add(&acct, &t->ioac);
} while (need_seqretry(&sig->stats_lock, seq));
done_seqretry_irqrestore(&sig->stats_lock, seq, flags);
rcu_read_unlock();
} else {
acct = task->ioac;
}