Dave Chinner <[email protected]> writes: > On Mon, Dec 03, 2012 at 01:53:39PM -0500, Jeff Moyer wrote: >> +static ssize_t cpu_list_store(struct device *dev, >> + struct device_attribute *attr, const char *buf, size_t count) >> +{ >> + struct backing_dev_info *bdi = dev_get_drvdata(dev); >> + struct bdi_writeback *wb = &bdi->wb; >> + cpumask_var_t newmask; >> + ssize_t ret; >> + struct task_struct *task; >> + >> + if (!alloc_cpumask_var(&newmask, GFP_KERNEL)) >> + return -ENOMEM; >> + >> + ret = cpulist_parse(buf, newmask); >> + if (!ret) { >> + spin_lock(&bdi->wb_lock); >> + task = wb->task; >> + if (task) >> + get_task_struct(task); >> + spin_unlock(&bdi->wb_lock); >> + if (task) { >> + ret = set_cpus_allowed_ptr(task, newmask); >> + put_task_struct(task); >> + } > > Why is this set here outside the bdi->flusher_cpumask_mutex?
The cpumask mutex protects updates to bdi->flusher_cpumask, it has nothing to do with the call to set_cpus_allowed. We are protected from concurrent calls to cpu_list_store by the sysfs mutex that is taken on entry. I understand that this is non-obvious, and it wouldn't be wrong to hold the mutex here. If you'd like me to do that for clarity, that would be ok with me. > Also, I'd prefer it named "..._lock" as that is the normal > convention for such variables. You can tell the type of lock from > the declaration or the use... I'm sure I can find counter-examples, but it doesn't really matter to me. I'll change it. >> @@ -437,6 +488,14 @@ static int bdi_forker_thread(void *ptr) >> spin_lock_bh(&bdi->wb_lock); >> bdi->wb.task = task; >> spin_unlock_bh(&bdi->wb_lock); >> + mutex_lock(&bdi->flusher_cpumask_mutex); >> + ret = set_cpus_allowed_ptr(task, >> + bdi->flusher_cpumask); >> + mutex_unlock(&bdi->flusher_cpumask_mutex); > > As it is set under the lock here.... It's done under the lock here since we need to keep bdi->flusher_cpumask from changing during the call to set_cpus_allowed. Cheers, Jeff -- 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/
