Messages in this thread | | | Date | Tue, 21 Apr 2015 10:07:00 -0400 (EDT) | From | Ulrich Obergfell <> | Subject | Re: [PATCH v9 2/3] watchdog: add watchdog_cpumask sysctl to assist nohz |
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Chris,
I think it would also be nice to check the plausibility of the user input.
+int proc_watchdog_cpumask(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int err; + + mutex_lock(&watchdog_proc_mutex); + err = proc_do_large_bitmap(table, write, buffer, lenp, ppos); + if (!err && write) { + /* Remove impossible cpus to keep sysctl output cleaner. */ + cpumask_and(watchdog_cpumask, watchdog_cpumask, + cpu_possible_mask); + + if (watchdog_enabled && watchdog_thresh) + smpboot_update_cpumask_percpu_thread(&watchdog_threads, + watchdog_cpumask); + } + mutex_unlock(&watchdog_proc_mutex); + return err; +}
I think the user should only be allowed to specify a mask that is a subset of tick_nohz_full_mask as only those CPUs don't have a watchdog thread by default. In other words, the user should not be able to interfere with housekeeping CPUs.
For example, add a plausibility check like so:
save watchdog_cpumask because proc_do_large_bitmap() is going to change it
proc_do_large_bitmap()
// return an error if the user-specified mask includes a housekeeping CPU if (watchdog_cpumask and 'negated tick_nohz_full_mask') { restore saved watchdog_cpumask return -EINVAL }
Regards,
Uli
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