From a2efdbf4fcb38ec1ae99c9d54d52c34fa867dc71 Mon Sep 17 00:00:00 2001 From: Eric W. Biederman Date: Fri, 28 Feb 2020 11:08:45 -0600 Subject: posix-cpu-timers: cpu_clock_sample_group() no longer needs siglock As of e78c3496790e ("time, signal: Protect resource use statistics with seqlock") cpu_clock_sample_group() no longer needs siglock protection so remove the stale comment. Signed-off-by: "Eric W. Biederman" Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/87eeuevduq.fsf@x220.int.ebiederm.org --- kernel/time/posix-cpu-timers.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'kernel/time/posix-cpu-timers.c') diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 8ff6da77a01f..46cc188bf5ab 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -336,9 +336,7 @@ static void __thread_group_cputime(struct task_struct *tsk, u64 *samples) /* * Sample a process (thread group) clock for the given task clkid. If the * group's cputime accounting is already enabled, read the atomic - * store. Otherwise a full update is required. Task's sighand lock must be - * held to protect the task traversal on a full update. clkid is already - * validated. + * store. Otherwise a full update is required. clkid is already validated. */ static u64 cpu_clock_sample_group(const clockid_t clkid, struct task_struct *p, bool start) -- cgit v1.2.3 From 60f2ceaa8111d9ec51af87bde4a6809f2b3235e4 Mon Sep 17 00:00:00 2001 From: Eric W. Biederman Date: Fri, 28 Feb 2020 11:09:19 -0600 Subject: posix-cpu-timers: Remove unnecessary locking around cpu_clock_sample_group As of e78c3496790e ("time, signal: Protect resource use statistics with seqlock") cpu_clock_sample_group no longers needs siglock protection. Unfortunately no one realized it at the time. Remove the extra locking that is for cpu_clock_sample_group and not for cpu_clock_sample. This significantly simplifies the code. Signed-off-by: "Eric W. Biederman" Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/878skmvdts.fsf@x220.int.ebiederm.org --- kernel/time/posix-cpu-timers.c | 66 ++++++++---------------------------------- 1 file changed, 12 insertions(+), 54 deletions(-) (limited to 'kernel/time/posix-cpu-timers.c') diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 46cc188bf5ab..40c2d8396bb9 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -718,31 +718,10 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp /* * Sample the clock to take the difference with the expiry time. */ - if (CPUCLOCK_PERTHREAD(timer->it_clock)) { + if (CPUCLOCK_PERTHREAD(timer->it_clock)) now = cpu_clock_sample(clkid, p); - } else { - struct sighand_struct *sighand; - unsigned long flags; - - /* - * Protect against sighand release/switch in exit/exec and - * also make timer sampling safe if it ends up calling - * thread_group_cputime(). - */ - sighand = lock_task_sighand(p, &flags); - if (unlikely(sighand == NULL)) { - /* - * The process has been reaped. - * We can't even collect a sample any more. - * Disarm the timer, nothing else to do. - */ - cpu_timer_setexpires(ctmr, 0); - return; - } else { - now = cpu_clock_sample_group(clkid, p, false); - unlock_task_sighand(p, &flags); - } - } + else + now = cpu_clock_sample_group(clkid, p, false); if (now < expires) { itp->it_value = ns_to_timespec64(expires - now); @@ -986,43 +965,22 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer) /* * Fetch the current sample and update the timer's expiry time. */ - if (CPUCLOCK_PERTHREAD(timer->it_clock)) { + if (CPUCLOCK_PERTHREAD(timer->it_clock)) now = cpu_clock_sample(clkid, p); - bump_cpu_timer(timer, now); - if (unlikely(p->exit_state)) - return; - - /* Protect timer list r/w in arm_timer() */ - sighand = lock_task_sighand(p, &flags); - if (!sighand) - return; - } else { - /* - * Protect arm_timer() and timer sampling in case of call to - * thread_group_cputime(). - */ - sighand = lock_task_sighand(p, &flags); - if (unlikely(sighand == NULL)) { - /* - * The process has been reaped. - * We can't even collect a sample any more. - */ - cpu_timer_setexpires(ctmr, 0); - return; - } else if (unlikely(p->exit_state) && thread_group_empty(p)) { - /* If the process is dying, no need to rearm */ - goto unlock; - } + else now = cpu_clock_sample_group(clkid, p, true); - bump_cpu_timer(timer, now); - /* Leave the sighand locked for the call below. */ - } + + bump_cpu_timer(timer, now); + + /* Protect timer list r/w in arm_timer() */ + sighand = lock_task_sighand(p, &flags); + if (unlikely(sighand == NULL)) + return; /* * Now re-arm for the new expiry time. */ arm_timer(timer); -unlock: unlock_task_sighand(p, &flags); } -- cgit v1.2.3 From beb41d9cbe4179058634e05d60235b6155c7b6c6 Mon Sep 17 00:00:00 2001 From: Eric W. Biederman Date: Fri, 28 Feb 2020 11:09:46 -0600 Subject: posix-cpu-timers: Pass the task into arm_timer() The task has been already computed to take siglock before calling arm_timer. So pass the benefit of that labor into arm_timer(). Signed-off-by: "Eric W. Biederman" Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/8736auvdt1.fsf@x220.int.ebiederm.org --- kernel/time/posix-cpu-timers.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) (limited to 'kernel/time/posix-cpu-timers.c') diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 40c2d8396bb9..ef936c5a910b 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -482,12 +482,11 @@ void posix_cpu_timers_exit_group(struct task_struct *tsk) * Insert the timer on the appropriate list before any timers that * expire later. This must be called with the sighand lock held. */ -static void arm_timer(struct k_itimer *timer) +static void arm_timer(struct k_itimer *timer, struct task_struct *p) { int clkidx = CPUCLOCK_WHICH(timer->it_clock); struct cpu_timer *ctmr = &timer->it.cpu; u64 newexp = cpu_timer_getexpires(ctmr); - struct task_struct *p = ctmr->task; struct posix_cputimer_base *base; if (CPUCLOCK_PERTHREAD(timer->it_clock)) @@ -660,7 +659,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags, */ cpu_timer_setexpires(ctmr, new_expires); if (new_expires != 0 && val < new_expires) { - arm_timer(timer); + arm_timer(timer, p); } unlock_task_sighand(p, &flags); @@ -980,7 +979,7 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer) /* * Now re-arm for the new expiry time. */ - arm_timer(timer); + arm_timer(timer, p); unlock_task_sighand(p, &flags); } -- cgit v1.2.3 From 55e8c8eb2c7b6bf30e99423ccfe7ca032f498f59 Mon Sep 17 00:00:00 2001 From: Eric W. Biederman Date: Fri, 28 Feb 2020 11:11:06 -0600 Subject: posix-cpu-timers: Store a reference to a pid not a task posix cpu timers do not handle the death of a process well. This is most clearly seen when a multi-threaded process calls exec from a thread that is not the leader of the thread group. The posix cpu timer code continues to pin the old thread group leader and is unable to find the siglock from there. This results in posix_cpu_timer_del being unable to delete a timer, posix_cpu_timer_set being unable to set a timer. Further to compensate for the problems in posix_cpu_timer_del on a multi-threaded exec all timers that point at the multi-threaded task are stopped. The code for the timers fundamentally needs to check if the target process/thread is alive. This needs an extra level of indirection. This level of indirection is already available in struct pid. So replace cpu.task with cpu.pid to get the needed extra layer of indirection. In addition to handling things more cleanly this reduces the amount of memory a timer can pin when a process exits and then is reaped from a task_struct to the vastly smaller struct pid. Fixes: e0a70217107e ("posix-cpu-timers: workaround to suppress the problems with mt exec") Signed-off-by: "Eric W. Biederman" Signed-off-by: Thomas Gleixner Link: https://lkml.kernel.org/r/87wo86tz6d.fsf@x220.int.ebiederm.org --- include/linux/posix-timers.h | 2 +- kernel/time/posix-cpu-timers.c | 73 +++++++++++++++++++++++++++++++----------- 2 files changed, 56 insertions(+), 19 deletions(-) (limited to 'kernel/time/posix-cpu-timers.c') diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h index 3d10c84a97a9..e3f0f8585da4 100644 --- a/include/linux/posix-timers.h +++ b/include/linux/posix-timers.h @@ -69,7 +69,7 @@ static inline int clockid_to_fd(const clockid_t clk) struct cpu_timer { struct timerqueue_node node; struct timerqueue_head *head; - struct task_struct *task; + struct pid *pid; struct list_head elist; int firing; }; diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index ef936c5a910b..6df468a622fe 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -118,6 +118,16 @@ static inline int validate_clock_permissions(const clockid_t clock) return __get_task_for_clock(clock, false, false) ? 0 : -EINVAL; } +static inline enum pid_type cpu_timer_pid_type(struct k_itimer *timer) +{ + return CPUCLOCK_PERTHREAD(timer->it_clock) ? PIDTYPE_PID : PIDTYPE_TGID; +} + +static inline struct task_struct *cpu_timer_task_rcu(struct k_itimer *timer) +{ + return pid_task(timer->it.cpu.pid, cpu_timer_pid_type(timer)); +} + /* * Update expiry time from increment, and increase overrun count, * given the current clock sample. @@ -391,7 +401,12 @@ static int posix_cpu_timer_create(struct k_itimer *new_timer) new_timer->kclock = &clock_posix_cpu; timerqueue_init(&new_timer->it.cpu.node); - new_timer->it.cpu.task = p; + 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); return 0; } @@ -404,13 +419,15 @@ static int posix_cpu_timer_create(struct k_itimer *new_timer) static int posix_cpu_timer_del(struct k_itimer *timer) { struct cpu_timer *ctmr = &timer->it.cpu; - struct task_struct *p = ctmr->task; struct sighand_struct *sighand; + struct task_struct *p; unsigned long flags; int ret = 0; - if (WARN_ON_ONCE(!p)) - return -EINVAL; + rcu_read_lock(); + p = cpu_timer_task_rcu(timer); + if (!p) + goto out; /* * Protect against sighand release/switch in exit/exec and process/ @@ -432,8 +449,10 @@ static int posix_cpu_timer_del(struct k_itimer *timer) unlock_task_sighand(p, &flags); } +out: + rcu_read_unlock(); if (!ret) - put_task_struct(p); + put_pid(ctmr->pid); return ret; } @@ -561,13 +580,21 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags, clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock); u64 old_expires, new_expires, old_incr, val; struct cpu_timer *ctmr = &timer->it.cpu; - struct task_struct *p = ctmr->task; struct sighand_struct *sighand; + struct task_struct *p; unsigned long flags; int ret = 0; - if (WARN_ON_ONCE(!p)) - return -EINVAL; + rcu_read_lock(); + p = cpu_timer_task_rcu(timer); + if (!p) { + /* + * If p has just been reaped, we can no + * longer get any information about it at all. + */ + rcu_read_unlock(); + return -ESRCH; + } /* * Use the to_ktime conversion because that clamps the maximum @@ -584,8 +611,10 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags, * If p has just been reaped, we can no * longer get any information about it at all. */ - if (unlikely(sighand == NULL)) + if (unlikely(sighand == NULL)) { + rcu_read_unlock(); return -ESRCH; + } /* * Disarm any old timer after extracting its expiry time. @@ -690,6 +719,7 @@ static int posix_cpu_timer_set(struct k_itimer *timer, int timer_flags, ret = 0; out: + rcu_read_unlock(); if (old) old->it_interval = ns_to_timespec64(old_incr); @@ -701,10 +731,12 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock); struct cpu_timer *ctmr = &timer->it.cpu; u64 now, expires = cpu_timer_getexpires(ctmr); - struct task_struct *p = ctmr->task; + struct task_struct *p; - if (WARN_ON_ONCE(!p)) - return; + rcu_read_lock(); + p = cpu_timer_task_rcu(timer); + if (!p) + goto out; /* * Easy part: convert the reload time. @@ -712,7 +744,7 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp itp->it_interval = ktime_to_timespec64(timer->it_interval); if (!expires) - return; + goto out; /* * Sample the clock to take the difference with the expiry time. @@ -732,6 +764,8 @@ static void posix_cpu_timer_get(struct k_itimer *timer, struct itimerspec64 *itp itp->it_value.tv_nsec = 1; itp->it_value.tv_sec = 0; } +out: + rcu_read_unlock(); } #define MAX_COLLECTED 20 @@ -952,14 +986,15 @@ static void check_process_timers(struct task_struct *tsk, static void posix_cpu_timer_rearm(struct k_itimer *timer) { clockid_t clkid = CPUCLOCK_WHICH(timer->it_clock); - struct cpu_timer *ctmr = &timer->it.cpu; - struct task_struct *p = ctmr->task; + struct task_struct *p; struct sighand_struct *sighand; unsigned long flags; u64 now; - if (WARN_ON_ONCE(!p)) - return; + rcu_read_lock(); + p = cpu_timer_task_rcu(timer); + if (!p) + goto out; /* * Fetch the current sample and update the timer's expiry time. @@ -974,13 +1009,15 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer) /* Protect timer list r/w in arm_timer() */ sighand = lock_task_sighand(p, &flags); if (unlikely(sighand == NULL)) - return; + goto out; /* * Now re-arm for the new expiry time. */ arm_timer(timer, p); unlock_task_sighand(p, &flags); +out: + rcu_read_unlock(); } /** -- cgit v1.2.3