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  1. Dec 31, 2009
    • Anton Vorontsov's avatar
      phylib: Fix deadlock on resume · 541cd3ee
      Anton Vorontsov authored
      
      
      Sometimes kernel hangs on resume with the following trace:
      
       ucc_geth e0102000.ucc: resume
       INFO: task bash:1764 blocked for more than 120 seconds.
       "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
       bash          D 0fecf43c     0  1764   1763 0x00000000
       Call Trace:
       [cf9a7c10] [c0012868] ret_from_except+0x0/0x14 (unreliable)
       --- Exception: cf9a7ce0 at __switch_to+0x4c/0x6c
           LR = 0xcf9a7cc0
       [cf9a7cd0] [c0008c14] __switch_to+0x4c/0x6c (unreliable)
       [cf9a7ce0] [c028bcfc] schedule+0x158/0x260
       [cf9a7d10] [c028c720] __mutex_lock_slowpath+0x80/0xd8
       [cf9a7d40] [c01cf388] phy_stop+0x20/0x70
       [cf9a7d50] [c01d514c] ugeth_resume+0x6c/0x13c
       [...]
      
      Here is why.
      
      On suspend:
      
      - PM core starts suspending devices, ucc_geth_suspend gets called;
      
      - ucc_geth calls phy_stop() on suspend. Note that phy_stop() is
        mostly asynchronous so it doesn't block ucc_geth's suspend routine,
        it just sets PHY_HALTED state and disables PHY's interrupts;
      
      - Suddenly the state machine gets scheduled, it grabs the phydev->lock
        mutex and tries to process the PHY_HALTED state, so it calls
        phydev->adjust_link(phydev->attached_dev). In ucc_geth case
        adjust_link() calls msleep(), which reschedules the code flow back to
        PM core, which now finishes suspend and so we end up sleeping with
        phydev->lock mutex held.
      
      On resume:
      
      - PM core starts resuming devices (notice that nobody rescheduled
        the state machine yet, so the mutex is still held), the core calls
        ucc_geth's resume routine;
      
      - ucc_geth_resume restarts the PHY with phy_stop()/phy_start()
        sequence, and the phy_*() calls are trying to grab the phydev->lock
        mutex. Here comes the deadlock.
      
      This patch fixes the issue by stopping the state machine on suspend
      and starting it again on resume.
      
      Signed-off-by: default avatarAnton Vorontsov <avorontsov@ru.mvista.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      541cd3ee
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