On Thu, Jan 07, 2021 at 11:08:39PM +0000, Satya Tangirala wrote: > > error = sb->s_op->freeze_super(sb); > > else > > @@ -600,6 +602,7 @@ int thaw_bdev(struct block_device *bdev) > > if (!sb) > > goto out; > > > > + bdev->bd_fsfreeze_sb = NULL; > This causes bdev->bd_fsfreeze_sb to be set to NULL even if the call to > thaw_super right after this line fail. So if a caller tries to call > thaw_bdev() again after receiving such an error, that next call won't even > try to call thaw_super(). Is that what we want here? (I don't know much > about this code, but from a cursory glance I think this difference is > visible to emergency_thaw_bdev() in fs/buffer.c) Yes, that definitively is an issue. > > I think the second difference (decrementing bd_fsfreeze_count when > get_active_super() returns NULL) doesn't change anything w.r.t the > use-after-free. It does however, change the behaviour of the function > slightly, and it might be caller visible (because from a cursory glance, it > looks like we're reading the bd_fsfreeze_count from some other places like > fs/super.c). Even before 040f04bd2e82, the code wouldn't decrement > bd_fsfreeze_count when get_active_super() returned NULL - so is this change > in behaviour intentional? And if so, maybe it should go in a separate > patch? Yes, that would be a change in behavior. And I'm not sure why we would want to change it. But if so we should do it in a separate patch that documents the why, on top of the patch that already is in the block tree.
