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  1. 11 Mar, 2011 1 commit
    • Lukas Czerner's avatar
      block: fix mis-synchronisation in blkdev_issue_zeroout() · 0aeea189
      Lukas Czerner authored 
      BZ29402
https://bugzilla.kernel.org/show_bug.cgi?id=29402

We can hit serious mis-synchronization in bio completion path of
blkdev_issue_zeroout() leading to a panic.

The problem is that when we are going to wait_for_completion() in
blkdev_issue_zeroout() we check if the bb.done equals issued (number of
submitted bios). If it does, we can skip the wait_for_completition()
and just out of the function since there is nothing to wait for.
However, there is a ordering problem because bio_batch_end_io() is
calling atomic_inc(&bb->done) before complete(), hence it might seem to
blkdev_issue_zeroout() that all bios has been completed and exit. At
this point when bio_batch_end_io() is going to call complete(bb->wait),
bb and wait does not longer exist since it was allocated on stack in
blkdev_issue_zeroout() ==> panic!

(thread 1)                      (thread 2)
bio_batch_end_io()              blkdev_issue_zeroout()
  if(bb) {                      ...
    if (bb->end_io)             ...
      bb->end_io(bio, err);     ...
    atomic_inc(&bb->done);      ...
    ...                         while (issued != atomic_read(&bb.done))
    ...                         (let issued == bb.done)
    ...                         (do the rest of the function)
    ...                         return ret;
    complete(bb->wait);
    ^^^^^^^^
    panic

We can fix this easily by simplifying bio_batch and completion counting.

Also remove bio_end_io_t *end_io since it is not used.
Signed-off-by: default avatarLukas Czerner <lczerner@redhat.com>
Reported-by: default avatarEric Whitney <eric.whitney@hp.com>
Tested-by: default avatarEric Whitney <eric.whitney@hp.com>
Reviewed-by: default avatarJeff Moyer <jmoyer@redhat.com>
CC: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: default avatarJens Axboe <jaxboe@fusionio.com>
      0aeea189
  3. 10 Mar, 2011 21 commits
  5. 09 Mar, 2011 16 commits
  7. 08 Mar, 2011 2 commits
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