• U
    watchdog: fix error handling in proc_watchdog_thresh() · d283c640
    Ulrich Obergfell 提交于
    The original watchdog_park_threads() function that was introduced by
    commit 81a4beef ("watchdog: introduce watchdog_park_threads() and
    watchdog_unpark_threads()") takes a very simple approach to handle
    errors returned by kthread_park(): It attempts to roll back all watchdog
    threads to the unparked state.  However, this may be undesired behaviour
    from the perspective of the caller which may want to handle errors as
    appropriate in its specific context.  Currently, there are two possible
    call chains:
    
    - watchdog suspend/resume interface
    
        lockup_detector_suspend
          watchdog_park_threads
    
    - write to parameters in /proc/sys/kernel
    
        proc_watchdog_update
          watchdog_enable_all_cpus
            update_watchdog_all_cpus
              watchdog_park_threads
    
    Instead of 'blindly' attempting to unpark the watchdog threads if a
    kthread_park() call fails, the new approach is to disable the lockup
    detectors in the above call chains.  Failure becomes visible to the user
    as follows:
    
    - error messages from lockup_detector_suspend()
                       or watchdog_enable_all_cpus()
    
    - the state that can be read from /proc/sys/kernel/watchdog_enabled
    
    - the 'write' system call in the latter call chain returns an error
    
    I did not experience kthread_park() failures in practice, I used some
    instrumentation to fake error returns from kthread_park() in order to test
    the patches.
    
    This patch (of 5):
    
    Restore the previous value of watchdog_thresh _and_ sample_period if
    proc_watchdog_update() returns an error.  The variables must be consistent
    to avoid false positives of the lockup detectors.
    Signed-off-by: NUlrich Obergfell <uobergfe@redhat.com>
    Reviewed-by: NAaron Tomlin <atomlin@redhat.com>
    Acked-by: NDon Zickus <dzickus@redhat.com>
    Cc: Ulrich Obergfell <uobergfe@redhat.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    d283c640
watchdog.c 27.2 KB