On Tue, Sep 18, 2012 at 08:51:47PM -0700, Hugh Dickins wrote:

In fuzzing with trinity, lockdep protested "possible irq lock inversion
dependency detected" when isolate_lru_page() reenabled interrupts while
still holding the supposedly irq-safe tree_lock:

invalidate_inode_pages2
  invalidate_complete_page2
    spin_lock_irq(&mapping->tree_lock)
    clear_page_mlock
      isolate_lru_page
        spin_unlock_irq(&zone->lru_lock)

isolate_lru_page() is correct to enable interrupts unconditionally:
invalidate_complete_page2() is incorrect to call clear_page_mlock()
while holding tree_lock, which is supposed to nest inside lru_lock.

Both truncate_complete_page() and invalidate_complete_page() call
clear_page_mlock() before taking tree_lock to remove page from
radix_tree.  I guess invalidate_complete_page2() preferred to test
PageDirty (again) under tree_lock before committing to the munlock;
but since the page has already been unmapped, its state is already
somewhat inconsistent, and no worse if clear_page_mlock() moved up.

Reported-by: Sasha Levin <redacted>
Deciphered-by: Andrew Morton [off-list ref]
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <redacted>
Cc: Rik van Riel <redacted>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michel Lespinasse <redacted>
Cc: Ying Han <redacted>
Cc: stable@vger.kernel.org

Acked-by: Mel Gorman <redacted>

-- 
Mel Gorman
SUSE Labs

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