linux-kernel - Race in wb_do

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Date:	Tue, 29 Jun 2010 16:28:16 -0400
From:	Larry Woodman <lwoodman@...hat.com>
To:	hch@...radead.org, linux-kernel@...r.kernel.org, riel@...hat.com
Subject: Race in wb_do_writeback() ???

Chistoph, I am seeing slabcache corruption.  wb_do_writeback() calls
wb_clear_pending() which can queue up the freeing of the bdi_work. Then
it calls wb_writeback() which can block, resulting in using the bdi_work
after its freed.

------------------------------------------------------------------
  /*
   * If this isn't a data integrity operation, just notify
   * that we have seen this work and we are now starting it.
   */
  if (!test_bit(WS_ONSTACK, &work->state))
         wb_clear_pending(wb, work);

  wrote += wb_writeback(wb, &args);

 /*
  * This is a data integrity writeback, so only do the
  * notification when we have completed the work.
  */
  if (test_bit(WS_ONSTACK, &work->state))
         wb_clear_pending(wb, work);
------------------------------------------------------------------

Can you have one unconditional call to wb_clear_pending() after the
calling wb_writeback()???

Larry

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