lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:   Thu, 28 Feb 2019 09:49:39 -0700
From:   Daniel Kurtz <>
To:     Greg Kroah-Hartman <>
Cc:, Mathias Nyman <>,
        "open list:USB XHCI DRIVER" <>,
        open list <>
Subject: Re: [PATCH] xhci: use iopoll for xhci_handshake

On Thu, Feb 28, 2019 at 12:09 AM Greg Kroah-Hartman
<> wrote:
> On Wed, Feb 27, 2019 at 03:19:17PM -0700, Daniel Kurtz wrote:
> > In cases such as xhci_abort_cmd_ring(), xhci_handshake() is called with
> > a spin lock held (and local interrupts disabled) with a huge 5 second
> > timeout.  This can translates to 5 million calls to udelay(1).  By its
> > very nature, udelay() is not meant to be precise, it only guarantees to
> > delay a minimum of 1 microsecond. Therefore the actual delay of
> > xhci_handshake() can be significantly longer.  If the average udelay(1)
> > is greater than 2.2 us, the total time in xhci_handshake() - with
> > interrupts disabled can be > 11 seconds triggering the kernel's soft lockup
> > detector.
> >
> > To avoid this, let's replace the open coded io polling loop with one from
> > iopoll.h that uses a loop timed with the more presumably reliable ktime
> > infrastructure.
> >
> > Signed-off-by: Daniel Kurtz <>
> Looks sane to me, nice fixup.
> Reviewed-by: Greg Kroah-Hartman <>
> Is this causing problems on older kernels/devices today such that we
> should backport this?

We detected that xhci_handshake timing out can lead to softlockup
while debugging a USB issue on a new product.  The xhci_handshake
timeout itself is a symptom of another underlying problem causing some
commands to be aborted.  I don't know if any such underlying problems
exist on other older devices, but the potential is there so a backport
is reasonable.  Although, it may just shift the symptom of an
underlying problem from a softlockup/oops to some other symptom, like
USB just being dead.


> thanks,
> greg k-h

Powered by blists - more mailing lists