• Mikulas Patocka's avatar
    dm snapshot: fix hung bios when copy error occurs · 385277bf
    Mikulas Patocka authored
    When there is an error copying a chunk dm-snapshot can incorrectly hold
    associated bios indefinitely, resulting in hung IO.
    The function copy_callback sets pe->error if there was error copying the
    chunk, and then calls complete_exception.  complete_exception calls
    pending_complete on error, otherwise it calls commit_exception with
    commit_callback (and commit_callback calls complete_exception).
    The persistent exception store (dm-snap-persistent.c) assumes that calls
    to prepare_exception and commit_exception are paired.
    persistent_prepare_exception increases ps->pending_count and
    persistent_commit_exception decreases it.
    If there is a copy error, persistent_prepare_exception is called but
    persistent_commit_exception is not.  This results in the variable
    ps->pending_count never returning to zero and that causes some pending
    exceptions (and their associated bios) to be held forever.
    Fix this by unconditionally calling commit_exception regardless of
    whether the copy was successful.  A new "valid" parameter is added to
    commit_exception -- when the copy fails this parameter is set to zero so
    that the chunk that failed to copy (and all following chunks) is not
    recorded in the snapshot store.  Also, remove commit_callback now that
    it is merely a wrapper around pending_complete.
    Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
    Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
    Cc: stable@vger.kernel.org
dm-snap-transient.c 3.66 KB