The patch titled
Subject: getrusage: move thread_group_cputime_adjusted() outside of lock_task_sighand()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
getrusage-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/getrusage-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.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: getrusage: move thread_group_cputime_adjusted() outside of lock_task_sighand()
Date: Fri, 19 Jan 2024 15:15:01 +0100
thread_group_cputime() does its own locking, we can safely shift
thread_group_cputime_adjusted() which does another for_each_thread loop
outside of ->siglock protected section.
This is also preparation for the next patch which changes getrusage() to
use stats_lock instead of siglock. Currently the deadlock is not
possible, if getrusage() enters the slow path and takes stats_lock,
read_seqretry() in thread_group_cputime() must always return 0, so
thread_group_cputime() will never try to take the same lock. Yet this
looks more safe and better performance-wise.
Link: https://lkml.kernel.org/r/20240119141501.GA23739@xxxxxxxxxx
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Tested-by: Dylan Hatch <dylanbhatch@xxxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Florent Revest <revest@xxxxxxxxxxxx>
Cc: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Helge Deller <deller@xxxxxx>
Cc: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Cc: Joey Gouly <joey.gouly@xxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Miguel Ojeda <ojeda@xxxxxxxxxx>
Cc: Mike Christie <michael.christie@xxxxxxxxxx>
Cc: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: Stefan Roesch <shr@xxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vincent Whitchurch <Vincent.Whitchurch@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/sys.c | 36 ++++++++++++++++++++----------------
1 file changed, 20 insertions(+), 16 deletions(-)
--- a/kernel/sys.c~getrusage-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand
+++ a/kernel/sys.c
@@ -1785,17 +1785,19 @@ void getrusage(struct task_struct *p, in
struct task_struct *t;
unsigned long flags;
u64 tgutime, tgstime, utime, stime;
- unsigned long maxrss = 0;
+ unsigned long maxrss;
+ struct mm_struct *mm;
struct signal_struct *sig = p->signal;
- memset((char *)r, 0, sizeof (*r));
+ memset(r, 0, sizeof(*r));
utime = stime = 0;
+ maxrss = 0;
if (who == RUSAGE_THREAD) {
task_cputime_adjusted(current, &utime, &stime);
accumulate_thread_rusage(p, r);
maxrss = sig->maxrss;
- goto out;
+ goto out_thread;
}
if (!lock_task_sighand(p, &flags))
@@ -1819,9 +1821,6 @@ void getrusage(struct task_struct *p, in
fallthrough;
case RUSAGE_SELF:
- thread_group_cputime_adjusted(p, &tgutime, &tgstime);
- utime += tgutime;
- stime += tgstime;
r->ru_nvcsw += sig->nvcsw;
r->ru_nivcsw += sig->nivcsw;
r->ru_minflt += sig->min_flt;
@@ -1839,19 +1838,24 @@ void getrusage(struct task_struct *p, in
}
unlock_task_sighand(p, &flags);
-out:
- r->ru_utime = ns_to_kernel_old_timeval(utime);
- r->ru_stime = ns_to_kernel_old_timeval(stime);
-
- if (who != RUSAGE_CHILDREN) {
- struct mm_struct *mm = get_task_mm(p);
+ if (who == RUSAGE_CHILDREN)
+ goto out_children;
- if (mm) {
- setmax_mm_hiwater_rss(&maxrss, mm);
- mmput(mm);
- }
+ thread_group_cputime_adjusted(p, &tgutime, &tgstime);
+ utime += tgutime;
+ stime += tgstime;
+
+out_thread:
+ mm = get_task_mm(p);
+ if (mm) {
+ setmax_mm_hiwater_rss(&maxrss, mm);
+ mmput(mm);
}
+
+out_children:
r->ru_maxrss = maxrss * (PAGE_SIZE / 1024); /* convert pages to KBs */
+ r->ru_utime = ns_to_kernel_old_timeval(utime);
+ r->ru_stime = ns_to_kernel_old_timeval(stime);
}
SYSCALL_DEFINE2(getrusage, int, who, struct rusage __user *, ru)
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
getrusage-move-thread_group_cputime_adjusted-outside-of-lock_task_sighand.patch
getrusage-use-sig-stats_lock.patch
