On Wed, 15 Jan 2014, atom...@redhat.com wrote:
> From: Aaron Tomlin <atom...@redhat.com>
>
> When khungtaskd detects hung tasks, it prints out
> backtraces from a number of those tasks. Sometimes
> the information on why things are stuck is hidden
> in those backtraces. Limiting the number of
> backtraces being printed out can result in the user
> not seeing the information necessary to debug the
> issue. This patch introduces an option to print an
> unlimited number of backtraces when khungtaskd
> detects hung tasks.
>
> While ULONG_MAX is practically "inf", this patch
> takes it one step further. Note: The maximum is
> now 2^31-1 (INT_MAX) which should hopefully be
> sufficient.
>
This rationale is someone cryptic, it seems what you're doing is allowing
the sysctl to be set to -1 that will never limit the number of warnings
and to do that you need a signed value so you converted ulong to int.
> Signed-off-by: Aaron Tomlin <atom...@redhat.com>
> ---
> include/linux/sched/sysctl.h | 2 +-
> kernel/hung_task.c | 6 ++++--
> kernel/sysctl.c | 5 +++--
> 3 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h
> index 41467f8..eb3c72d7 100644
> --- a/include/linux/sched/sysctl.h
> +++ b/include/linux/sched/sysctl.h
> @@ -5,7 +5,7 @@
> extern int sysctl_hung_task_check_count;
> extern unsigned int sysctl_hung_task_panic;
> extern unsigned long sysctl_hung_task_timeout_secs;
> -extern unsigned long sysctl_hung_task_warnings;
> +extern int sysctl_hung_task_warnings;
> extern int proc_dohung_task_timeout_secs(struct ctl_table *table, int write,
> void __user *buffer,
> size_t *lenp, loff_t *ppos);
> diff --git a/kernel/hung_task.c b/kernel/hung_task.c
> index 9328b80..0b9c169 100644
> --- a/kernel/hung_task.c
> +++ b/kernel/hung_task.c
> @@ -37,7 +37,7 @@ int __read_mostly sysctl_hung_task_check_count =
> PID_MAX_LIMIT;
> */
> unsigned long __read_mostly sysctl_hung_task_timeout_secs =
> CONFIG_DEFAULT_HUNG_TASK_TIMEOUT;
>
> -unsigned long __read_mostly sysctl_hung_task_warnings = 10;
> +int __read_mostly sysctl_hung_task_warnings = 10;
>
> static int __read_mostly did_panic;
>
> @@ -98,7 +98,9 @@ static void check_hung_task(struct task_struct *t, unsigned
> long timeout)
>
> if (!sysctl_hung_task_warnings)
> return;
> - sysctl_hung_task_warnings--;
> +
> + if (sysctl_hung_task_warnings > 0)
> + sysctl_hung_task_warnings--;
>
> /*
> * Ok, the task did not get scheduled for more than 2 minutes,
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index dd531a6..b50cd13 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -985,9 +985,10 @@ static struct ctl_table kern_table[] = {
> {
> .procname = "hung_task_warnings",
> .data = &sysctl_hung_task_warnings,
> - .maxlen = sizeof(unsigned long),
> + .maxlen = sizeof(int),
> .mode = 0644,
> - .proc_handler = proc_doulongvec_minmax,
> + .proc_handler = proc_dointvec_minmax,
> + .extra1 = &neg_one,
> },
> #endif
> #ifdef CONFIG_COMPAT
hung_task_warnings isn't documented in the source, so how is anybody
supposed to know that -1 is an acceptable value and what it's special case
allows?
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