Oleg Nesterov wrote:
> If we need the urgent hack to fix the regression, then I suggest to change
> scsi_host_alloc() temporary until mptsas (or whatever) is fixed.
Device initialization taking longer than 30 seconds is possible and is not a
hang up. It is systemd which needs to be fixed.
> --- x/drivers/scsi/hosts.c
> +++ x/drivers/scsi/hosts.c
> @@ -447,8 +447,18 @@ struct Scsi_Host *scsi_host_alloc(struct
> dev_set_name(&shost->shost_dev, "host%d", shost->host_no);
> shost->shost_dev.groups = scsi_sysfs_shost_attr_groups;
>
> - shost->ehandler = kthread_run(scsi_error_handler, shost,
> - "scsi_eh_%d", shost->host_no);
> + /*
> + * HUGE COMMENT. and kthread_create() needs s/ENOMEM/EINTR/.
> + */
> + for (;;) {
> + shost->ehandler = kthread_run(scsi_error_handler, shost,
> + "scsi_eh_%d", shost->host_no);
> + if (!IS_ERR(shost->ehandler) || PTR_ERR(shost->ehandler) != -EINTR)
> + break;
> + clear_thread_flag(TIF_SIGPENDING);
> + }
> + recalc_sigpending();
> +
> if (IS_ERR(shost->ehandler)) {
> printk(KERN_WARNING "scsi%d: error handler thread failed to spawn, error = %ld\n",
> shost->host_no, PTR_ERR(shost->ehandler));
>
>
I think we need a bit different version, in order to take TIF_MEMDIE flag into
account at the caller of kthread_create(), for the purpose of commit 786235ee
is "try to die as soon as possible if chosen by the OOM killer".
for (;;) {
shost->ehandler = kthread_run(scsi_error_handler, shost,
"scsi_eh_%d", shost->host_no);
if (PTR_ERR(shost->ehandler) != -EINTR ||
test_thread_flag(TIF_MEMDIE))
break;
clear_thread_flag(TIF_SIGPENDING);
}
recalc_sigpending();
But I have two worrying points.
(1) Changing return code from -ENOMEM to -EINTR may not be sufficient.
If kmalloc(GFP_KERNEL) in kthread_create_on_node() does something that
calls recalc_sigpending(), TIF_SIGPENDING will be set on the second call
to kthread_run(). This will make wait_for_completion_killable() return
-EINTR immediately because the second call to kthread_run() happens only
when current thread already received SIGKILL (by other than the OOM
killer). This may form an infinite busy loop.
As I think it is difficult to prove that kmalloc(GFP_KERNEL) never sets
TIF_SIGPENDING flag, we would need to call
clear_thread_flag(TIF_SIGPENDING) immediately before
wait_for_completion_killable() and call recalc_sigpending() immediately
after wait_for_completion_killable(). Is this better than taking care of
SIGKILL (by other than the OOM killer) on the first call to
kthread_run() ?
(2) I don't like scattering around test_thread_flag(TIF_MEMDIE), for there
might be other drivers who receive SIGKILL by systemd's 30 seconds
timeout.
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