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    Subject[RFC 1/2] watchdog: update watchdog attributes atomically
    Date
    proc_dowatchdog doesn't synchronize multiple callers which
    might lead to confusion when two parallel callers might confuse
    watchdog_enable_all_cpus resp. watchdog_disable_all_cpus (e.g. watchdog
    gets enabled even if watchdog_thresh was set to 0 already).

    This patch adds a local mutex which synchronizes callers to the sysctl
    handler.

    Signed-off-by: Michal Hocko <mhocko@suse.cz>
    ---
    kernel/watchdog.c | 7 +++++--
    1 file changed, 5 insertions(+), 2 deletions(-)

    diff --git a/kernel/watchdog.c b/kernel/watchdog.c
    index 1241d8c..2d64c02 100644
    --- a/kernel/watchdog.c
    +++ b/kernel/watchdog.c
    @@ -520,13 +520,15 @@ int proc_dowatchdog(struct ctl_table *table, int write,
    void __user *buffer, size_t *lenp, loff_t *ppos)
    {
    int err, old_thresh, old_enabled;
    + static DEFINE_MUTEX(watchdog_proc_mutex);

    + mutex_lock(&watchdog_proc_mutex);
    old_thresh = ACCESS_ONCE(watchdog_thresh);
    old_enabled = ACCESS_ONCE(watchdog_user_enabled);

    err = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
    if (err || !write)
    - return err;
    + goto out;

    set_sample_period();
    /*
    @@ -544,7 +546,8 @@ int proc_dowatchdog(struct ctl_table *table, int write,
    watchdog_thresh = old_thresh;
    watchdog_user_enabled = old_enabled;
    }
    -
    +out:
    + mutex_unlock(&watchdog_proc_mutex);
    return err;
    }
    #endif /* CONFIG_SYSCTL */
    --
    1.8.3.2


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