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  1. Dec 22, 2019
    • Jan Stancek's avatar
      pipe: fix empty pipe check in pipe_write() · 0dd1e377
      Jan Stancek authored
      
      LTP pipeio_1 test is hanging with v5.5-rc2-385-gb8e382a185eb,
      with read side observing empty pipe and sleeping and write
      side running out of space and then sleeping as well. In this
      scenario there are 5 writers and 1 reader.
      
      Problem is that after pipe_write() reacquires pipe lock, it
      re-checks for empty pipe with potentially stale 'head' and
      doesn't wake up read side anymore. pipe->tail can advance
      beyond 'head', because there are multiple writers.
      
      Use pipe->head for empty pipe check after reacquiring lock
      to observe current state.
      
      Testing: With patch, LTP pipeio_1 ran successfully in loop for 1 hour.
               Without patch it hanged within a minute.
      
      Fixes: 1b6b26ae ("pipe: fix and clarify pipe write wakeup logic")
      Reported-by: default avatarRachel Sibley <rasibley@redhat.com>
      Signed-off-by: default avatarJan Stancek <jstancek@redhat.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      0dd1e377
  2. Dec 21, 2019
  3. Dec 20, 2019
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