On Thu, May 07, 2015 at 05:17:45PM -0700, Brian Norris wrote:
> On Thu, May 07, 2015 at 05:10:12PM -0700, Brian Norris wrote:
> > On Tue, Apr 21, 2015 at 12:20:22PM +0200, Giuseppe Cantavenera wrote:
> > > @@ -484,7 +486,7 @@ int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
> > > if (old->open) {
> > > if (old->tr->release)
> > > old->tr->release(old);
> > > - __put_mtd_device(old->mtd);
> > > + put_mtd_device(old->mtd);
> >
> > This looks wrong. See:
> [...]
> > deregister_mtd_blktrans()
> > |_ mutex_lock(&mtd_table_mutex)
> > |_ tr->remove_dev() -> inftl_remove_dev()
> > |_ del_mtd_blktrans_dev()
> > |_ put_mtd_device()
> > |_ mutex_lock(&mtd_table_mutex) <--- AA deadlock
>
> What's more, this code in del_mtd_blktrans_dev() makes it obvious that
> this hunk is wrong:
>
> int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
> {
> unsigned long flags;
>
> if (mutex_trylock(&mtd_table_mutex)) {
> mutex_unlock(&mtd_table_mutex);
> BUG();
> }
> ...
>
> So rather than a comment, the code is showing that it's a BUG() to not
> be holding mtd_table_mutex already.
As an alternative to your patch, how about the following?
BTW, this does still leave a usecount race in
drivers/mtd/maps/vmu-flash.c. But that driver should really be using
mtd->_get_device(), if it actually wants its own refcount.
Signed-off-by: Brian Norris <computersforpeace@xxxxxxxxx>
---
diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 2b0c52870999..df7c6c70757a 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -197,6 +197,7 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
return -ERESTARTSYS; /* FIXME: busy loop! -arnd*/
mutex_lock(&dev->lock);
+ mutex_lock(&mtd_table_mutex);
if (dev->open)
goto unlock;
@@ -220,6 +221,7 @@ static int blktrans_open(struct block_device *bdev, fmode_t mode)
unlock:
dev->open++;
+ mutex_unlock(&mtd_table_mutex);
mutex_unlock(&dev->lock);
blktrans_dev_put(dev);
return ret;
@@ -230,6 +232,7 @@ error_release:
error_put:
module_put(dev->tr->owner);
kref_put(&dev->ref, blktrans_dev_release);
+ mutex_unlock(&mtd_table_mutex);
mutex_unlock(&dev->lock);
blktrans_dev_put(dev);
return ret;
@@ -243,6 +246,7 @@ static void blktrans_release(struct gendisk *disk, fmode_t mode)
return;
mutex_lock(&dev->lock);
+ mutex_lock(&mtd_table_mutex);
if (--dev->open)
goto unlock;
@@ -256,6 +260,7 @@ static void blktrans_release(struct gendisk *disk, fmode_t mode)
__put_mtd_device(dev->mtd);
}
unlock:
+ mutex_unlock(&mtd_table_mutex);
mutex_unlock(&dev->lock);
blktrans_dev_put(dev);
}
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