On Thu, May 26, 2016 at 8:06 AM, Qu Wenruo <quwen...@cn.fujitsu.com> wrote: > Since the we are using atomic and wait queue for block group > reservations and it's not controlled by lockdep, we need pay much more > attention to any modification to write path. > > Or it's very easy to under flow block group reservations and cause lock > balance.
Ok, have you observed this happening in practice? There's nothing wrong with adding this warning, but it makes me curious why you do it only here, specially if you haven't experienced a bug. That is, there are other places (some recent others not so recent) where we use an atomic for waiting and waking up. Also the patch subject "btrfs: Add debug warning for new block group reservations" is very confusing. You meant to say something like "Add warning when decrementing a block group's reservations counter". thanks > > Add warning on for dec_block_group_reservations() if the reservations is > already minus. > > Although such warning doesn't always catch the directly caller, but should > provides good enough clue for later debug. > > Signed-off-by: Qu Wenruo <quwen...@cn.fujitsu.com> > --- > v2: > Fix compile error > Change to WARN_ON_ONCE(), as when it underflows, it will always under > flow > --- > fs/btrfs/extent-tree.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c > index 9424864..47ce96b 100644 > --- a/fs/btrfs/extent-tree.c > +++ b/fs/btrfs/extent-tree.c > @@ -6243,6 +6243,7 @@ void btrfs_dec_block_group_reservations(struct > btrfs_fs_info *fs_info, > ASSERT(bg); > if (atomic_dec_and_test(&bg->reservations)) > wake_up_atomic_t(&bg->reservations); > + WARN_ON_ONCE(atomic_read(&bg->reservations) < 0); > btrfs_put_block_group(bg); > } > > -- > 2.8.3 > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
