linux-kernel - Re: [PATCH] xhci: use iopoll for xhci

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Message-ID: <20190228070950.GB27446@kroah.com>
Date:   Thu, 28 Feb 2019 08:09:50 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Daniel Kurtz <djkurtz@...omium.org>
Cc:     rrangel@...omium.org, Mathias Nyman <mathias.nyman@...el.com>,
        "open list:USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] xhci: use iopoll for xhci_handshake

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 <djkurtz@...omium.org>

Looks sane to me, nice fixup.

Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

Is this causing problems on older kernels/devices today such that we
should backport this?

thanks,

greg k-h