jsauer/torvalds-linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2026-01-11 17:10:13 +00:00
Code

seqlock, procfs: Match scoped_seqlock_read() critical section vs. RCU ordering in do_task_stat() to do_io_accounting()

Browse Source 
There's two patterns of taking the RCU read-lock and the
sig->stats_lock read-seqlock in do_task_stat() and
do_io_accounting(), with a different ordering:

	# do_io_accounting():

	guard(rcu)();
	scoped_seqlock_read (&sig->stats_lock, ss_lock_irqsave) {

	# do_task_stat():

	scoped_seqlock_read (&sig->stats_lock, ss_lock_irqsave) {
	...
			rcu_read_lock();

The ordering is RCU-read+seqlock_read in the first
case, seqlock_read+RCU-read in the second case.

While technically these read locks can be taken in any order,
nevertheless it's good practice to use the more intrusive lock
on the inside (which is the IRQs-off section in this case),
and reduces head-scratching during review when done consistently,
so let's use the do_io_accounting() pattern in do_task_stat().

This will also reduce irqs-off latencies in do_task_stat() a tiny bit.

Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Link: https://patch.msgid.link/aS6rwnaPbHFCdHp1@gmail.com
This commit is contained in:
Ingo Molnar 2025-12-02 10:05:10 +01:00
parent 4a26e7032d
commit 24bc5ea5c0
1 changed files with 17 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
fs/proc/array.c
View File

@ -537,27 +537,27 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
if (permitted && (!whole || num_threads < 2))
wchan = !task_is_running(task);
scoped_seqlock_read (&sig->stats_lock, ss_lock_irqsave) {
cmin_flt = sig->cmin_flt;
cmaj_flt = sig->cmaj_flt;
cutime = sig->cutime;
cstime = sig->cstime;
cgtime = sig->cgtime;
scoped_guard(rcu) {
scoped_seqlock_read (&sig->stats_lock, ss_lock_irqsave) {
cmin_flt = sig->cmin_flt;
cmaj_flt = sig->cmaj_flt;
cutime = sig->cutime;
cstime = sig->cstime;
cgtime = sig->cgtime;
if (whole) {
struct task_struct *t;
if (whole) {
struct task_struct *t;
min_flt = sig->min_flt;
maj_flt = sig->maj_flt;
gtime = sig->gtime;
min_flt = sig->min_flt;
maj_flt = sig->maj_flt;
gtime = sig->gtime;
rcu_read_lock();
__for_each_thread(sig, t) {
min_flt += t->min_flt;
maj_flt += t->maj_flt;
gtime += task_gtime(t);
__for_each_thread(sig, t) {
min_flt += t->min_flt;
maj_flt += t->maj_flt;
gtime += task_gtime(t);
}
}
rcu_read_unlock();
}
}