[PATCH 4.19 34/41] getrusage: move thread_group_cputime_adjusted() outside of lock_task_sighand()

Sasha Levin
2024-03-13T17:05:16Z

From: Oleg Nesterov <oleg@redhat.com>

[ Upstream commit daa694e4137571b4ebec330f9a9b4d54aa8b8089 ]

Patch series "getrusage: use sig->stats_lock", v2.

This patch (of 2):

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, thread_group_cputime() takes the same
lock. With the current implementation recursive read_seqbegin_or_lock()
is fine, thread_group_cputime() can't enter the slow mode if the caller
holds stats_lock, yet this looks more safe and better performance-wise.

Link: https://lkml.kernel.org/r/20240122155023.GA26169@redhat.com
Link: https://lkml.kernel.org/r/20240122155050.GA26205@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Dylan Hatch <dylanbhatch@google.com>
Tested-by: Dylan Hatch <dylanbhatch@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/sys.c | 34 +++++++++++++++++++---------------
1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index d0d4f4c586518..ab621d7837c97 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1717,17 +1717,19 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
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))
@@ -1750,9 +1752,6 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
break;

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;
@@ -1772,19 +1771,24 @@ void getrusage(struct task_struct *p, int who, struct rusage *r)
}
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)
+ goto out_children;

- if (who != RUSAGE_CHILDREN) {
- struct mm_struct *mm = get_task_mm(p);
+ thread_group_cputime_adjusted(p, &tgutime, &tgstime);
+ utime += tgutime;
+ stime += tgstime;

- if (mm) {
- setmax_mm_hiwater_rss(&maxrss, mm);
- mmput(mm);
- }
+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)
--
2.43.0