2018-04-17 21:59:10

by Laura Abbott

[permalink] [raw]
Subject: [PATCH] posix-cpu-timers: Ensure set_process_cpu_timer is always evaluated

Commit a9445e47d897 ("posix-cpu-timers: Make set_process_cpu_timer()
more robust") moved the check into the 'if' statement. Unfortunately,
it did so on the right side of an && which means that it may get short
circuited and never evaluated. This is easily reproduced with:

$ cat loop.c
void main() {
struct rlimit res;
/* set the CPU time limit */
getrlimit(RLIMIT_CPU,&res);
res.rlim_cur = 2;
res.rlim_max = 2;
setrlimit(RLIMIT_CPU,&res);

while (1);
}

Which will hang forever instead of being killed. Fix this by pulling the
evaluation out of the if statement but checking the return value instead.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1568337
Fixes: a9445e47d897 ("posix-cpu-timers: Make set_process_cpu_timer() more robust")
Signed-off-by: Laura Abbott <[email protected]>
---
kernel/time/posix-cpu-timers.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index ec9f5da6f163..9cfa7f907654 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1187,10 +1187,12 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
u64 *newval, u64 *oldval)
{
u64 now;
+ int ret;

WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED);
+ ret = cpu_timer_sample_group(clock_idx, tsk, &now);

- if (oldval && cpu_timer_sample_group(clock_idx, tsk, &now) != -EINVAL) {
+ if (oldval && ret != -EINVAL) {
/*
* We are setting itimer. The *oldval is absolute and we update
* it to be relative, *newval argument is relative and we update
--
2.17.0



Subject: [tip:timers/urgent] posix-cpu-timers: Ensure set_process_cpu_timer is always evaluated

Commit-ID: c3bca5d450b620dd3d36e14b5e1f43639fd47d6b
Gitweb: https://git.kernel.org/tip/c3bca5d450b620dd3d36e14b5e1f43639fd47d6b
Author: Laura Abbott <[email protected]>
AuthorDate: Tue, 17 Apr 2018 14:57:42 -0700
Committer: Thomas Gleixner <[email protected]>
CommitDate: Thu, 19 Apr 2018 12:54:57 +0200

posix-cpu-timers: Ensure set_process_cpu_timer is always evaluated

Commit a9445e47d897 ("posix-cpu-timers: Make set_process_cpu_timer()
more robust") moved the check into the 'if' statement. Unfortunately,
it did so on the right side of an && which means that it may get short
circuited and never evaluated. This is easily reproduced with:

$ cat loop.c
void main() {
struct rlimit res;
/* set the CPU time limit */
getrlimit(RLIMIT_CPU,&res);
res.rlim_cur = 2;
res.rlim_max = 2;
setrlimit(RLIMIT_CPU,&res);

while (1);
}

Which will hang forever instead of being killed. Fix this by pulling the
evaluation out of the if statement but checking the return value instead.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1568337
Fixes: a9445e47d897 ("posix-cpu-timers: Make set_process_cpu_timer() more robust")
Signed-off-by: Laura Abbott <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: "Max R . P . Grossmann" <[email protected]>
Cc: John Stultz <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

---
kernel/time/posix-cpu-timers.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 2541bd89f20e..5a6251ac6f7a 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -1205,10 +1205,12 @@ void set_process_cpu_timer(struct task_struct *tsk, unsigned int clock_idx,
u64 *newval, u64 *oldval)
{
u64 now;
+ int ret;

WARN_ON_ONCE(clock_idx == CPUCLOCK_SCHED);
+ ret = cpu_timer_sample_group(clock_idx, tsk, &now);

- if (oldval && cpu_timer_sample_group(clock_idx, tsk, &now) != -EINVAL) {
+ if (oldval && ret != -EINVAL) {
/*
* We are setting itimer. The *oldval is absolute and we update
* it to be relative, *newval argument is relative and we update