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| author |   Barret Rhoden <brho@google.com> | 2022-01-06 12:20:41 -0500 |
|---|---|---|
| committer |   Eric W. Biederman <ebiederm@xmission.com> | 2022-03-08 14:33:36 -0600 |
| commit | 18c91bb2d87268d23868bf13508f5bc9cf04e89a (patch) | |
| tree | e081820aafeec498f7d81513d6ec7411972ab1f9 /include/linux/posix-timers.h | |
| parent | prlimit: make do_prlimit() static (diff) | |
| download | linux-dev-18c91bb2d87268d23868bf13508f5bc9cf04e89a.tar.xz linux-dev-18c91bb2d87268d23868bf13508f5bc9cf04e89a.zip | |
prlimit: do not grab the tasklist_lock
Unnecessarily grabbing the tasklist_lock can be a scalability bottleneck
for workloads that also must grab the tasklist_lock for waiting,
killing, and cloning.
The tasklist_lock was grabbed to protect tsk->sighand from disappearing
(becoming NULL). tsk->signal was already protected by holding a
reference to tsk.
update_rlimit_cpu() assumed tsk->sighand != NULL. With this commit, it
attempts to lock_task_sighand(). However, this means that
update_rlimit_cpu() can fail. This only happens when a task is exiting.
Note that during exec, sighand may *change*, but it will not be NULL.
Prior to this commit, the do_prlimit() ensured that update_rlimit_cpu()
would not fail by read locking the tasklist_lock and checking tsk->sighand
!= NULL.
If update_rlimit_cpu() fails, there may be other tasks that are not
exiting that share tsk->signal. However, the group_leader is the last
task to be released, so if we cannot update_rlimit_cpu(group_leader),
then the entire process is exiting.
The only other caller of update_rlimit_cpu() is
selinux_bprm_committing_creds(). It has tsk == current, so
update_rlimit_cpu() cannot fail (current->sighand cannot disappear
until current exits).
This change resulted in a 14% speedup on a microbenchmark where parents
kill and wait on their children, and children getpriority, setpriority,
and getrlimit.
Signed-off-by: Barret Rhoden <brho@google.com>
Link: https://lkml.kernel.org/r/20220106172041.522167-4-brho@google.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Diffstat (limited to 'include/linux/posix-timers.h')
| -rw-r--r-- | include/linux/posix-timers.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h index 5bbcd280bfd2..9cf126c3b27f 100644 --- a/include/linux/posix-timers.h +++ b/include/linux/posix-timers.h @@ -253,7 +253,7 @@ void posix_cpu_timers_exit_group(struct task_struct *task); void set_process_cpu_timer(struct task_struct *task, unsigned int clock_idx, u64 *newval, u64 *oldval); -void update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new); +int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new); void posixtimer_rearm(struct kernel_siginfo *info); #endif |