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Date: Wed, 24 Apr 2024 15:49:50 -0700
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: Guenter Roeck <linux@roeck-us.net>, linux-usb@vger.kernel.org,
	linux-kernel@vger.kernel.org, Gerd Hoffmann <kraxel@redhat.com>
Subject: Re: [PATCH v2] usb: ohci: Prevent missed ohci interrupts
Message-ID: <2024042441-salutary-finishing-f54d@gregkh>
References: <20240424195951.3749388-1-linux@roeck-us.net>
 <0a29cc85-a79e-476d-aae6-0a054aad2e90@rowland.harvard.edu>
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In-Reply-To: <0a29cc85-a79e-476d-aae6-0a054aad2e90@rowland.harvard.edu>

On Wed, Apr 24, 2024 at 06:30:06PM -0400, Alan Stern wrote:
> On Wed, Apr 24, 2024 at 12:59:51PM -0700, Guenter Roeck wrote:
> > Testing ohci functionality with qemu's pci-ohci emulation often results
> > in ohci interface stalls, resulting in hung task timeouts.
> > 
> > The problem is caused by lost interrupts between the emulation and the
> > Linux kernel code. Additional interrupts raised while the ohci interrupt
> > handler in Linux is running and before the handler clears the interrupt
> > status are not handled. The fix for a similar problem in ehci suggests
> > that the problem is likely caused by edge-triggered MSI interrupts. See
> > commit 0b60557230ad ("usb: ehci: Prevent missed ehci interrupts with
> > edge-triggered MSI") for details.
> > 
> > Ensure that the ohci interrupt code handles all pending interrupts before
> > returning to solve the problem.
> > 
> > Cc: Gerd Hoffmann <kraxel@redhat.com>
> > Fixes: 306c54d0edb6 ("usb: hcd: Try MSI interrupts on PCI devices")
> > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > ---
> > v2: Only repeat if the interface is still active
> 
> Reviewed-by: Alan Stern <stern@rowland.harvard.edu>
> 
> Greg might insist that the patch be CC'ed to stable@vger.kernel.org since 
> it contains a Fixes: tag.

I'll add that by hand, no worries.