From: Alan Stern <stern@rowland.harvard.edu>
To: Sam Sun <samsun1006219@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
Greg KH <gregkh@linuxfoundation.org>,
swboyd@chromium.org, ricardo@marliere.net, hkallweit1@gmail.com,
heikki.krogerus@linux.intel.com, mathias.nyman@linux.intel.com,
royluo@google.com, syzkaller-bugs@googlegroups.com,
xrivendell7@gmail.com
Subject: Re: [Linux kernel bug] general protection fault in disable_store
Date: Fri, 12 Apr 2024 14:11:49 -0400 [thread overview]
Message-ID: <69a6f4c9-6470-40d1-99f1-aaf532497d02@rowland.harvard.edu> (raw)
In-Reply-To: <CAEkJfYMjO+vMBGPcaLa51gjeKxFAJBrSa0t_iJUtauQD3DaK8w@mail.gmail.com>
On Sat, Apr 13, 2024 at 12:26:07AM +0800, Sam Sun wrote:
> On Fri, Apr 12, 2024 at 10:40 PM Alan Stern <stern@rowland.harvard.edu> wrote:
> > I suspect the usb_hub_to_struct_hub() call is racing with the
> > spinlock-protected region in hub_disconnect() (in hub.c).
> >
> > > If there is any other thing I could help, please let me know.
> >
> > Try the patch below. It should eliminate that race, which hopefully
> > will fix the problem.
> I applied this patch and tried to execute several times, no more
> kernel core dump in my environment. I think this bug is fixed by the
> patch. But I do have one more question about it. Since it is a data
> race bug, it has reproducibility issues originally. How can I confirm
> if a racy bug is fixed by test? This kind of bug might still have a
> race window but is harder to trigger. Just curious, not for this
> patch. I think this patch eliminates the racy window.
If you don't what what is racing, then testing cannot prove that a race
is eliminated. However, if you do know where a race occurs then it's
easy to see how mutual exclusion can prevent the race from happening.
In this case the bug might have had a different cause, something other
than a race between usb_hub_to_struct_hub() and hub_disconnect(). If
that's so then testing this patch would not be a definite proof that the
bug is gone. But if that race _is_ the cause of the bug then this patch
will fix it -- you can see that just by reading the code with no need
for testing.
Besides, the patch is needed in any case because that race certainly
_can_ occur. And maybe not only on this pathway.
May I add your "Reported-and-tested-by:" to the patch?
Alan Stern
next prev parent reply other threads:[~2024-04-12 18:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-11 6:52 [Linux kernel bug] general protection fault in disable_store Sam Sun
2024-04-11 6:58 ` Greg KH
2024-04-11 7:19 ` Sam Sun
2024-04-11 15:24 ` Alan Stern
2024-04-12 13:08 ` Sam Sun
2024-04-12 14:40 ` Alan Stern
2024-04-12 16:26 ` Sam Sun
2024-04-12 18:11 ` Alan Stern [this message]
2024-04-12 18:32 ` Alan Stern
2024-04-13 5:08 ` Sam Sun
2024-04-15 14:47 ` Alan Stern
2024-04-16 9:05 ` Sam Sun
2024-04-16 16:35 ` Alan Stern
2024-04-17 7:39 ` Sam Sun
2024-04-17 14:23 ` Alan Stern
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