On Sun, Mar 25, 2007 at 12:50:25PM -0700, Paul Jackson wrote: > Is there perhaps another race here?
Yes, we have! Modified patch below. Compile/boot tested on a x86_64 box. Currently cpuset_exit() changes the exiting task's ->cpuset pointer w/o taking task_lock(). This can lead to ugly races between attach_task and cpuset_exit. Details of the races are described at http://lkml.org/lkml/2007/3/24/132. Patch below closes those races. It is against 2.6.21-rc4 and has undergone a simple compile/boot test on a x86_64 box. Signed-off-by : Srivatsa Vaddagiri <[EMAIL PROTECTED]> --- 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 2007-03-26 16:48:24.000000000 +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_to_be_released = NULL; 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_to_be_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_to_be_released) + check_for_release(oldcs_to_be_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). @@ -2241,20 +2240,23 @@ void cpuset_fork(struct task_struct *chi void cpuset_exit(struct task_struct *tsk) { struct cpuset *cs; + struct cpuset *oldcs_to_be_released = NULL; + task_lock(tsk); cs = tsk->cpuset; tsk->cpuset = &top_cpuset; /* the_top_cpuset_hack - see above */ + if (atomic_dec_and_test(&cs->count)) + oldcs_to_be_released = cs; + task_unlock(tsk); if (notify_on_release(cs)) { char *pathbuf = NULL; mutex_lock(&manage_mutex); - if (atomic_dec_and_test(&cs->count)) - check_for_release(cs, &pathbuf); + if (oldcs_to_be_released) + check_for_release(oldcs_to_be_released, &pathbuf); mutex_unlock(&manage_mutex); cpuset_release_agent(pathbuf); - } else { - atomic_dec(&cs->count); } } _ -- Regards, vatsa - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
