From 9bf7c32409354b4a2fa3207d369a22c8233f718c Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Sat, 25 Apr 2020 18:38:54 -0500 Subject: posix-cpu-timers: Extend rcu_read_lock removing task_struct references 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" --- kernel/time/posix-cpu-timers.c | 43 ++++++++++++++++++++++-------------------- 1 file changed, 23 insertions(+), 20 deletions(-) (limited to 'kernel/time') diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index b7f972fb115e..91996dd089a4 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -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; } -- cgit v1.2.3-58-ga151