• Jeff Mahoney's avatar
    btrfs: delalloc for page dirtied out-of-band in fixup worker · 87826df0
    Jeff Mahoney authored
     We encountered an issue that was easily observable on s/390 systems but
     could really happen anywhere. The timing just seemed to hit reliably
     on s/390 with limited memory.
     The gist is that when an unexpected set_page_dirty() happened, we'd
     run into the BUG() in btrfs_writepage_fixup_worker since it wasn't
     properly set up for delalloc.
     This patch does the following:
     - Performs the missing delalloc in the fixup worker
     - Allow the start hook to return -EBUSY which informs __extent_writepage
       that it should mark the page skipped and not to redirty it. This is
       required since the fixup worker can fail with -ENOSPC and the page
       will have already been redirtied. That causes an Oops in
       drop_outstanding_extents later. Retrying the fixup worker could
       lead to an infinite loop. Deferring the page redirty also saves us
       some cycles since the page would be stuck in a resubmit-redirty loop
       until the fixup worker completes. It's not harmful, just wasteful.
     - If the fixup worker fails, we mark the page and mapping as errored,
       and end the writeback, similar to what we would do had the page
       actually been submitted to writeback.
    Signed-off-by: default avatarJeff Mahoney <jeffm@suse.com>
extent_io.h 11.8 KB