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Date: Sun, 25 Mar 2007 23:22:15 +0530 From: Balbir Singh <balbir@...ibm.com> To: vatsa@...ibm.com CC: pj@....com, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] Fix race between attach_task and cpuset_exit Hi, Vatsa, Srivatsa Vaddagiri wrote: > > diff -puN kernel/cpuset.c~cpuset_race_fix kernel/cpuset.c > --- linux-2.6.21-rc4/kernel/cpuset.c~cpuset_race_fix 2007-03-25 21:08:27.000000000 +0530 > +++ linux-2.6.21-rc4-vatsa/kernel/cpuset.c 2007-03-25 21:25:05.000000000 +0530 > @@ -1182,6 +1182,7 @@ static int attach_task(struct cpuset *cs > pid_t pid; > struct task_struct *tsk; > struct cpuset *oldcs; > + struct cpuset *oldcs_tobe_released = NULL; How about oldcs_to_be_released? > cpumask_t cpus; > nodemask_t from, to; > struct mm_struct *mm; > @@ -1237,6 +1238,8 @@ static int attach_task(struct cpuset *cs > } > atomic_inc(&cs->count); > rcu_assign_pointer(tsk->cpuset, cs); > + if (atomic_dec_and_test(&oldcs->count)) > + oldcs_tobe_released = oldcs; > task_unlock(tsk); > > guarantee_online_cpus(cs, &cpus); > @@ -1257,8 +1260,8 @@ static int attach_task(struct cpuset *cs > > put_task_struct(tsk); > synchronize_rcu(); > - if (atomic_dec_and_test(&oldcs->count)) > - check_for_release(oldcs, ppathbuf); > + if (oldcs_tobe_released) > + check_for_release(oldcs_tobe_released, ppathbuf); > return 0; > } > > @@ -2200,10 +2203,6 @@ void cpuset_fork(struct task_struct *chi > * it is holding that mutex while calling check_for_release(), > * which calls kmalloc(), so can't be called holding callback_mutex(). > * > - * We don't need to task_lock() this reference to tsk->cpuset, > - * because tsk is already marked PF_EXITING, so attach_task() won't > - * mess with it, or task is a failed fork, never visible to attach_task. > - * > * the_top_cpuset_hack: > * > * Set the exiting tasks cpuset to the root cpuset (top_cpuset). > @@ -2242,19 +2241,20 @@ void cpuset_exit(struct task_struct *tsk > { > struct cpuset *cs; > > + task_lock(tsk); > cs = tsk->cpuset; > tsk->cpuset = &top_cpuset; /* the_top_cpuset_hack - see above */ > + atomic_dec(&cs->count); How about using a local variable like ref_count and using ref_count = atomic_dec_and_test(&cs->count); This will avoid the two atomic operations, atomic_dec() and atomic_read() below. > + task_unlock(tsk); > > if (notify_on_release(cs)) { > char *pathbuf = NULL; > > mutex_lock(&manage_mutex); > - if (atomic_dec_and_test(&cs->count)) > + if (!atomic_read(&cs->count)) if (ref_count == 0) > check_for_release(cs, &pathbuf); > mutex_unlock(&manage_mutex); > cpuset_release_agent(pathbuf); > - } else { > - atomic_dec(&cs->count); > } > } > -- Warm Regards, Balbir Singh Linux Technology Center IBM, ISTL - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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