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posix-cpu-timers: Extend rcu_read_lock removing task_struct references

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Now that the code stores of pid references it is no longer necessary
or desirable to take a reference on task_struct in __get_task_for_clock.

Instead extend the scope of rcu_read_lock and remove the reference
counting on struct task_struct entirely.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
This commit is contained in:
Eric W. Biederman 2020-04-25 18:38:54 -05:00
parent bbd40fc481
commit 9bf7c32409
1 changed files with 23 additions and 20 deletions
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43
kernel/time/posix-cpu-timers.c
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@ -81,36 +81,36 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread,
}
static struct task_struct *__get_task_for_clock(const clockid_t clock,
bool getref, bool gettime)
bool gettime)
{
const bool thread = !!CPUCLOCK_PERTHREAD(clock);
const pid_t pid = CPUCLOCK_PID(clock);
struct task_struct *p;
if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
return NULL;
rcu_read_lock();
p = lookup_task(pid, thread, gettime);
if (p && getref)
get_task_struct(p);
rcu_read_unlock();
return p;
return lookup_task(pid, thread, gettime);
}
static inline struct task_struct *get_task_for_clock(const clockid_t clock)
{
return __get_task_for_clock(clock, true, false);
return __get_task_for_clock(clock, false);
}
static inline struct task_struct *get_task_for_clock_get(const clockid_t clock)
{
return __get_task_for_clock(clock, true, true);
return __get_task_for_clock(clock, true);
}
static inline int validate_clock_permissions(const clockid_t clock)
{
return __get_task_for_clock(clock, false, false) ? 0 : -EINVAL;
int ret;
rcu_read_lock();
ret = __get_task_for_clock(clock, false) ? 0 : -EINVAL;
rcu_read_unlock();
return ret;
}
static inline enum pid_type cpu_timer_pid_type(struct k_itimer *timer)
@ -368,15 +368,18 @@ static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
struct task_struct *tsk;
u64 t;
rcu_read_lock();
tsk = get_task_for_clock_get(clock);
if (!tsk)
if (!tsk) {
rcu_read_unlock();
return -EINVAL;
}
if (CPUCLOCK_PERTHREAD(clock))
t = cpu_clock_sample(clkid, tsk);
else
t = cpu_clock_sample_group(clkid, tsk, false);
put_task_struct(tsk);
rcu_read_unlock();
*tp = ns_to_timespec64(t);
return 0;
@ -389,19 +392,19 @@ static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
*/
static int posix_cpu_timer_create(struct k_itimer *new_timer)
{
struct task_struct *p = get_task_for_clock(new_timer->it_clock);
struct task_struct *p;
if (!p)
rcu_read_lock();
p = get_task_for_clock(new_timer->it_clock);
if (!p) {
rcu_read_unlock();
return -EINVAL;
}
new_timer->kclock = &clock_posix_cpu;
timerqueue_init(&new_timer->it.cpu.node);
new_timer->it.cpu.pid = get_task_pid(p, cpu_timer_pid_type(new_timer));
/*
* get_task_for_clock() took a reference on @p. Drop it as the timer
* holds a reference on the pid of @p.
*/
put_task_struct(p);
rcu_read_unlock();
return 0;
}