linux-kernel - Re: please fix FUSION (Was: [v3.13][v3.14][Regression]kthread:makekthread

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Message-ID: <1395521330.2143.51.camel@dabdike.int.hansenpartnership.com>
Date:	Sat, 22 Mar 2014 13:48:50 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	joseph.salisbury@...onical.com, Nagalakshmi.Nandigama@....com,
	Sreekanth.Reddy@....com, rientjes@...gle.com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	tj@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	kernel-team@...ts.ubuntu.com, linux-scsi@...r.kernel.org,
	thenzl@...hat.com
Subject: Re: please fix FUSION (Was:
 [v3.13][v3.14][Regression]kthread:makekthread_create()killable)

On Sat, 2014-03-22 at 20:25 +0100, Oleg Nesterov wrote:
> On 03/22, Tetsuo Handa wrote:
> >
> > Oleg Nesterov wrote:
> > > Tetsuo, what do you think?
> >
> > I don't like blocking SIGKILL while doing operations that depend on memory
> > allocation by other processes. If the OOM killer is triggered and it chose
> > the process blocking SIGKILL in mptsas_init() (I know it unlikely happens),
> > it generates the OOM killer deadlock.
> 
> It seems that we do not understand each other.
> 
> I do not like this hack too. And it is even wrong, you can't really block
> SIGKILL. And it is unnecessary in a sense that (I think) it is fine that
> module_init() reacts to SIGKILL and aborts, just the fact it crashes the
> kernel in the error paths is not fine.
> 
> The driver should be fixed anyway. As for timeout, either userspace/systemd
> should be changed to not send SIGKILL after 30 secs, or (better) the driver
> should be changed to not waste 30 secs.
> 
> The hack I sent can only serve as a short term solution, it should be
> reverted once we have something better. And, otoh, this hack only affects
> the problematic driver which should be fixed in any case.
> 
> Do you see my point? I can be wrong, but I think that you constantly
> misunderstand the intent.
> 
> > My preference is to fix kthread_create() to handle SIGKILL gracefully.
> 
> And now I do not understand you too. I do not understand why should we
> "fix" kthread_create().
> 
> > Many kernel operations (e.g. mutex_lock() wait_event() wait_for_completion())
> > ignore SIGKILL and the current users depend on SIGKILL being ignored. Thus,
> > commit 786235ee sounds like a kernel API breakage.
> 
> Personally I do not really think so, but OK. In this case lets revert
> 786235ee.
> 
> > Commit 786235ee "kthread: make kthread_create() killable" changed to
> > leave kthread_create() as soon as receiving SIGKILL. But this change
> > caused boot failures because systemd-udevd receives SIGKILL due to timeout
> > while loading SCSI controller drivers using finit_module() [1].
> 
> And I still think that 786235ee simply uncovered the problems in this
> driver. Perhaps we should change kthread_create() for some reason, but
> (imho) not because we need to help the buggy code.
> 
> > Therefore, this patch changes kthread_create() from "wait forever in
> > killable state" to "wait for 10 seconds in unkillable state, check for
> > the OOM killer every second".
> 
> Personally I dislike this change. In fact I think it is ugly. But this
> is only my opinion.
> 
> If you convince someone to take this patch I won't argue.

OK, the fix from the SCSI point of view is to make the mpt teardown path
actually work.  The whole thing looks to be a complete mess because
there's another place where it will do the wrong thing in
mptscsih_remove().  You always have to call mpt_detach() otherwise the
device doesn't get removed from the lists.  In theory this patch fixes
both bugs in the driver.

James

---

diff --git a/drivers/message/fusion/mptscsih.c b/drivers/message/fusion/mptscsih.c
index 727819c..282d39a 100644
--- a/drivers/message/fusion/mptscsih.c
+++ b/drivers/message/fusion/mptscsih.c
@@ -1176,10 +1176,14 @@ mptscsih_remove(struct pci_dev *pdev)
 	MPT_SCSI_HOST		*hd;
 	int sz1;
 
+	if (!host)
+		/* not brought up far enough to do scsi_host_attach() */
+		goto out;
+
 	scsi_remove_host(host);
 
 	if((hd = shost_priv(host)) == NULL)
-		return;
+		goto out;
 
 	mptscsih_shutdown(pdev);
 
@@ -1203,6 +1207,7 @@ mptscsih_remove(struct pci_dev *pdev)
 
 	scsi_host_put(host);
 
+ out:
 	mpt_detach(pdev);
 
 }


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