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Limit number of tasks shown in taskq proc

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To prevent holding tq_lock for too long.

Before zfsonlinux/zfs@8e71ab9, hogging delay tasks and cat /proc/spl/taskq
would easily cause a lockup. While that bug has been fixed. It's probably
still a good idea to do this just in case task lists grow too large.

Reviewed-by: Tim Chase <tim@chase2k.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #586
This commit is contained in:
Chunwei Chen 2016-12-01 10:06:27 -08:00 committed by Brian Behlendorf
parent cbba714667
commit 493492559e
2 changed files with 28 additions and 6 deletions
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15
man/man5/spl-module-parameters.5
View File

@ -326,3 +326,18 @@ configurations.
.sp
Default value: \fB4\fR
.RE
.sp
.ne 2
.na
\fBspl_max_show_tasks\fR (uint)
.ad
.RS 12n
The maximum number of tasks per pending list in each taskq shown in
/proc/spl/{taskq,taskq-all}. Write 0 to turn off the limit. The proc file will
walk the lists with lock held, reading it could cause a lock up if the list
grow too large without limiting the output. "(truncated)" will be shown if the
list is larger than the limit.
.sp
Default value: \fB512\fR
.RE

19
module/spl/spl-proc.c
View File

@ -234,6 +234,10 @@ taskq_seq_show_headers(struct seq_file *f)
#define LHEAD_ACTIVE 4
#define LHEAD_SIZE 5
static unsigned int spl_max_show_tasks = 512;
module_param(spl_max_show_tasks, uint, 0644);
MODULE_PARM_DESC(spl_max_show_tasks, "Max number of tasks shown in taskq proc");
static int
taskq_seq_show_impl(struct seq_file *f, void *p, boolean_t allflag)
{
@ -308,16 +312,20 @@ taskq_seq_show_impl(struct seq_file *f, void *p, boolean_t allflag)
if (lheads[i]) {
j = 0;
list_for_each(lh, lheads[i]) {
if (spl_max_show_tasks != 0 &&
j >= spl_max_show_tasks) {
seq_printf(f, "\n\t(truncated)");
break;
}
/* show the wait waitq list */
if (i == LHEAD_WAIT) {
wq = list_entry(lh, wait_queue_t, task_list);
if (j == 0)
seq_printf(f, "\t%s:",
list_names[i]);
else if (j == 12) {
else if (j % 8 == 0)
seq_printf(f, "\n\t ");
j = 0;
}
tsk = wq->private;
seq_printf(f, " %d", tsk->pid);
/* pend, prio and delay lists */
@ -327,10 +335,9 @@ taskq_seq_show_impl(struct seq_file *f, void *p, boolean_t allflag)
if (j == 0)
seq_printf(f, "\t%s:",
list_names[i]);
else if (j == 2) {
else if (j % 2 == 0)
seq_printf(f, "\n\t ");
j = 0;
}
seq_printf(f, " %pf(%ps)",
tqe->tqent_func,
tqe->tqent_arg);