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Subject[PATCH v3 07/27] core: optimize setrlimit for current task
Date
From: Jiri Slaby <jirislaby@gmail.com>

Don't take tasklist lock for 'current'. It's not needed, since
current->sighand/signal can't disappear.

This improves serlimit called especially via sys_setrlimit.

Signed-off-by: Jiri Slaby <jirislaby@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
---
kernel/sys.c | 16 ++++++++++------
1 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 3082eaf..605ab9c 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1250,11 +1250,14 @@ int setrlimit(struct task_struct *tsk, unsigned int resource,
if (resource == RLIMIT_NOFILE && new_rlim->rlim_max > sysctl_nr_open)
return -EPERM;

- /* protect tsk->signal and tsk->sighand from disappearing */
- read_lock(&tasklist_lock);
- if (!tsk->sighand) {
- retval = -ESRCH;
- goto out;
+ /* optimization: 'current' doesn't need locking, e.g. setrlimit */
+ if (tsk != current) {
+ /* protect tsk->signal and tsk->sighand from disappearing */
+ read_lock(&tasklist_lock);
+ if (!tsk->sighand) {
+ retval = -ESRCH;
+ goto out;
+ }
}

retval = security_task_setrlimit(tsk, resource, new_rlim);
@@ -1294,7 +1297,8 @@ int setrlimit(struct task_struct *tsk, unsigned int resource,

update_rlimit_cpu(tsk, new_rlim->rlim_cur);
out:
- read_unlock(&tasklist_lock);
+ if (tsk != current)
+ read_unlock(&tasklist_lock);
return retval;
}

--
1.6.5.3


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