The patch titled
Subject: do_io_accounting: use sig->stats_lock
has been added to the -mm mm-nonmm-unstable branch. Its filename is
do_io_accounting-use-sig-stats_lock.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/do_io_accounting-use-sig-stats_lock.patch
This patch will later appear in the mm-nonmm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Oleg Nesterov <oleg@xxxxxxxxxx>
Subject: do_io_accounting: use sig->stats_lock
Date: Mon, 23 Oct 2023 17:34:05 +0200
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@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/proc/base.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
--- a/fs/proc/base.c~do_io_accounting-use-sig-stats_lock
+++ a/fs/proc/base.c
@@ -2973,7 +2973,6 @@ static const struct file_operations proc
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_
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;
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
do_io_accounting-use-__for_each_thread.patch
do_io_accounting-use-sig-stats_lock.patch
