Theodore Tso wrote:
> On Thu, Jun 11, 2009 at 07:14:36PM +0200, Frederic Weisbecker wrote:
>> For the filters, we could enter the text name which would be
>> internally converted into a dev_t, there should be no problem.
>>
>> Also the raw dev_t can be stored and then human-friendly printed on
>> print time.
>>
>> Both seem about trivial to add.
>
> If someone wants to take this code and drop it into the core tracing
> code, please feel free.
>
Just notice this code has been merge, but there are 2 bugs in it.
> - Ted
>
> /*
> * jbd2_dev_to_name is a utility function used by the jbd2 and ext4
> * tracing infrastructure to map a dev_t to a device name.
> *
> * The caller should use rcu_read_lock() in order to make sure the
> * device name stays valid until its done with it. We use
> * rcu_read_lock() as well to make sure we're safe in case the caller
> * gets sloppy, and because rcu_read_lock() is cheap and can be safely
> * nested.
> */
> struct devname_cache {
> struct rcu_head rcu;
> dev_t device;
> char devname[BDEVNAME_SIZE];
> };
> #define CACHE_SIZE_BITS 6
> static struct devname_cache *devcache[1 << CACHE_SIZE_BITS];
> static DEFINE_SPINLOCK(devname_cache_lock);
>
> static void free_devcache(struct rcu_head *rcu)
> {
> kfree(rcu);
> }
>
> const char *jbd2_dev_to_name(dev_t device)
> {
> int i = hash_32(device, CACHE_SIZE_BITS);
> char *ret;
> struct block_device *bd;
>
> rcu_read_lock();
> if (devcache[i] && devcache[i]->device == device) {
> ret = devcache[i]->devname;
> rcu_read_unlock();
> return ret;
It doesn't seem safe to dereference @ret outside rcu read section.
> }
> rcu_read_unlock();
>
> spin_lock(&devname_cache_lock);
> if (devcache[i]) {
> if (devcache[i]->device == device) {
> ret = devcache[i]->devname;
> spin_unlock(&devname_cache_lock);
> return ret;
> }
> call_rcu(&devcache[i]->rcu, free_devcache);
> }
> devcache[i] = kmalloc(sizeof(struct devname_cache), GFP_KERNEL);
kmalloc(GFP_KERNEL) called with spin_lock held..
> if (!devcache[i]) {
> spin_unlock(&devname_cache_lock);
> return "NODEV-ALLOCFAILURE"; /* Something non-NULL */
> }
> devcache[i]->device = device;
> bd = bdget(device);
> if (bd) {
> bdevname(bd, devcache[i]->devname);
> bdput(bd);
> } else
> __bdevname(device, devcache[i]->devname);
> ret = devcache[i]->devname;
> spin_unlock(&devname_cache_lock);
> return ret;
> }
> EXPORT_SYMBOL(jbd2_dev_to_name);
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