locking problems: Btrfs: be more selective in the defrag ioctl

[Dan Carpenter]

Hi Chris,

There is a locking problem in
940100a4a7b78 "Btrfs: be more selective in the defrag ioctl"

There are two places where we break out of the while loop under the
lock.

fs/btrfs/ioctl.c +708 btrfs_defrag_file(159) error: double lock 'mutex:&inode->i_mutex'
600 mutex_lock(&inode->i_mutex);
601 if (range->flags & BTRFS_DEFRAG_RANGE_COMPRESS)
602 BTRFS_I(inode)->force_compress = 1;
603
604 ret = btrfs_check_data_free_space(root, inode, PAGE_CACHE_SIZE);
605 if (ret) {
606 ret = -ENOSPC;
607 break;

Here.

608 }
609
610 ret = btrfs_reserve_metadata_for_delalloc(root, inode, 1);
611 if (ret) {
612 btrfs_free_reserved_data_space(root, inode,
613 PAGE_CACHE_SIZE);
614 ret = -ENOSPC;
615 break;

And here.

616 }

Maybe we should have "goto err_reservations;" instead of break? I
don't know the code well enough to say.

regards,
dan carpenter
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[Josef Bacik]

No, everything is accounted for correctly. If the metadata reservation fails,
we free the data space reservation and break. If the data space reservation
fails, we're good to go and can just exit. Thanks,

Josef

[Dan Carpenter]

What about the lock on line 606?

> > 600 mutex_lock(&inode->i_mutex);

If we break on line 615 or 607 that means that we return with the lock
held, or if (range->flags & BTRFS_DEFRAG_RANGE_COMPRESS) is true then we
dead lock.

regards,
dan carpenter

[Josef Bacik]

Ahh yeah you are right, should probably just put a mutex_unlock before the break
in both cases. Thanks,