Messages in this thread Patch in this message | | | From | Waiman Long <> | Subject | [PATCH v7 4/5] sched: Handle set_cpus_allowed_ptr() & sched_setaffinity() race | Date | Fri, 2 Sep 2022 11:25:55 -0400 |
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Racing is possible between set_cpus_allowed_ptr() and sched_setaffinity() or between multiple sched_setaffinity() calls from different CPUs. To resolve these race conditions, we need to update both user_cpus_ptr and cpus_mask in a single lock critical section instead of separated ones. This requires moving the user_cpus_ptr update to set_cpus_allowed_common().
The SCA_USER flag will be used to signify that a user_cpus_ptr update will have to be done. The new user_cpus_ptr will be put into the a percpu variable pending_user_mask at the beginning of the lock crtical section. The pending user mask will then be taken up in set_cpus_allowed_common().
Ideally, user_cpus_ptr should only be updated if the sched_setaffinity() is successful. However, this patch will update user_cpus_ptr when the first call to __set_cpus_allowed_ptr() is successful. However, if there is racing between sched_setaffinity() and cpuset update, the subsequent calls to __set_cpus_allowed_ptr() may fail but the user_cpus_ptr will still be updated in this corner case. A warning will be printed in this corner case.
Signed-off-by: Waiman Long <longman@redhat.com> --- kernel/sched/core.c | 59 ++++++++++++++++++++++++++++----------------- 1 file changed, 37 insertions(+), 22 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 84544daf3839..618341d0fa51 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -111,6 +111,7 @@ EXPORT_TRACEPOINT_SYMBOL_GPL(sched_util_est_se_tp); EXPORT_TRACEPOINT_SYMBOL_GPL(sched_update_nr_running_tp); DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues); +DEFINE_PER_CPU(struct cpumask **, pending_user_mask); #ifdef CONFIG_SCHED_DEBUG /* @@ -2199,6 +2200,7 @@ __do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask, u32 static int __set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask, + struct cpumask **puser_mask, u32 flags); static void migrate_disable_switch(struct rq *rq, struct task_struct *p) @@ -2249,7 +2251,8 @@ void migrate_enable(void) */ preempt_disable(); if (p->cpus_ptr != &p->cpus_mask) - __set_cpus_allowed_ptr(p, &p->cpus_mask, SCA_MIGRATE_ENABLE); + __set_cpus_allowed_ptr(p, &p->cpus_mask, NULL, + SCA_MIGRATE_ENABLE); /* * Mustn't clear migration_disabled() until cpus_ptr points back at the * regular cpus_mask, otherwise things that race (eg. @@ -2538,6 +2541,12 @@ void set_cpus_allowed_common(struct task_struct *p, const struct cpumask *new_ma cpumask_copy(&p->cpus_mask, new_mask); p->nr_cpus_allowed = cpumask_weight(new_mask); + + /* + * Swap in the new user_cpus_ptr if SCA_USER flag set + */ + if (flags & SCA_USER) + swap(p->user_cpus_ptr, *__this_cpu_read(pending_user_mask)); } static void @@ -2926,12 +2935,19 @@ static int __set_cpus_allowed_ptr_locked(struct task_struct *p, * call is not atomic; no spinlocks may be held. */ static int __set_cpus_allowed_ptr(struct task_struct *p, - const struct cpumask *new_mask, u32 flags) + const struct cpumask *new_mask, + struct cpumask **puser_mask, + u32 flags) { struct rq_flags rf; struct rq *rq; rq = task_rq_lock(p, &rf); + /* + * CPU won't be preempted or interrupted while holding task_rq_lock(). + */ + __this_cpu_write(pending_user_mask, puser_mask); + if (p->user_cpus_ptr && !(flags & SCA_USER) && cpumask_and(rq->scratch_mask, new_mask, p->user_cpus_ptr)) new_mask = rq->scratch_mask; @@ -2941,7 +2957,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask) { - return __set_cpus_allowed_ptr(p, new_mask, 0); + return __set_cpus_allowed_ptr(p, new_mask, NULL, 0); } EXPORT_SYMBOL_GPL(set_cpus_allowed_ptr); @@ -3032,7 +3048,8 @@ void force_compatible_cpus_allowed_ptr(struct task_struct *p) } static int -__sched_setaffinity(struct task_struct *p, const struct cpumask *mask, int flags); +__sched_setaffinity(struct task_struct *p, const struct cpumask *mask, + struct cpumask **puser_mask, int flags); /* * Restore the affinity of a task @p which was previously restricted by a @@ -3049,7 +3066,7 @@ void relax_compatible_cpus_allowed_ptr(struct task_struct *p) * Try to restore the old affinity mask with __sched_setaffinity(). * Cpuset masking will be done there too. */ - ret = __sched_setaffinity(p, task_user_cpus(p), 0); + ret = __sched_setaffinity(p, task_user_cpus(p), NULL, 0); WARN_ON_ONCE(ret); } @@ -3529,6 +3546,7 @@ void sched_set_stop_task(int cpu, struct task_struct *stop) static inline int __set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask, + struct cpumask *user_mask, u32 flags) { return set_cpus_allowed_ptr(p, new_mask); @@ -8053,7 +8071,8 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask) #endif static int -__sched_setaffinity(struct task_struct *p, const struct cpumask *mask, int flags) +__sched_setaffinity(struct task_struct *p, const struct cpumask *mask, + struct cpumask **puser_mask, int flags) { int retval; cpumask_var_t cpus_allowed, new_mask; @@ -8072,8 +8091,10 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask, int flags retval = dl_task_check_affinity(p, new_mask); if (retval) goto out_free_new_mask; + + retval = __set_cpus_allowed_ptr(p, new_mask, puser_mask, + SCA_CHECK | flags); again: - retval = __set_cpus_allowed_ptr(p, new_mask, SCA_CHECK | flags); if (retval) goto out_free_new_mask; @@ -8084,6 +8105,14 @@ __sched_setaffinity(struct task_struct *p, const struct cpumask *mask, int flags * Just reset the cpumask to the cpuset's cpus_allowed. */ cpumask_copy(new_mask, cpus_allowed); + retval = __set_cpus_allowed_ptr(p, new_mask, NULL, SCA_CHECK); + + /* + * Warn in case of the unexpected success in updating + * user_cpus_ptr in first __set_cpus_allowed_ptr() but then + * fails in a subsequent retry. + */ + WARN_ON_ONCE(retval && (flags | SCA_USER)); goto again; } @@ -8138,21 +8167,7 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask) } cpumask_copy(user_mask, in_mask); - retval = __sched_setaffinity(p, in_mask, SCA_USER); - - /* - * Save in_mask into user_cpus_ptr after a successful - * __sched_setaffinity() call. pi_lock is used to synchronize - * changes to user_cpus_ptr. - */ - if (!retval) { - unsigned long flags; - - /* Use pi_lock to synchronize changes to user_cpus_ptr */ - raw_spin_lock_irqsave(&p->pi_lock, flags); - swap(p->user_cpus_ptr, user_mask); - raw_spin_unlock_irqrestore(&p->pi_lock, flags); - } + retval = __sched_setaffinity(p, in_mask, &user_mask, SCA_USER); kfree(user_mask); out_put_task: -- 2.31.1
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