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From: Alan Stern <stern@rowland.harvard.edu>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Valentina Manea <valentina.manea.m@gmail.com>,
	Shuah Khan <shuah@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	USB list <linux-usb@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Dmitry Vyukov <dvyukov@google.com>,
	Nazime Hande Harputluoglu <handeharputlu@google.com>,
	syzkaller <syzkaller@googlegroups.com>
Subject: Re: Is usb_hcd_giveback_urb() allowed in task context?
Date: Mon, 5 Oct 2020 11:22:18 -0400	[thread overview]
Message-ID: <20201005152218.GF376584@rowland.harvard.edu> (raw)
In-Reply-To: <CAAeHK+wb4k-LGTjK9F5YbJNviF_+yU+wE_=Vpo9Rn7KFN8vG6Q@mail.gmail.com>

On Mon, Oct 05, 2020 at 05:08:11PM +0200, Andrey Konovalov wrote:
> Dear USB and USB/IP maintainers,
> 
> While fuzzing the USB/IP stack with syzkaller we've stumbled upon an issue.
> 
> Currently kcov (the subsystem that is used for coverage collection)
> USB-related callbacks assume that usb_hcd_giveback_urb() can only be
> called from interrupt context, as indicated by the comment before the
> function definition.

The primary reason for this restriction (as far as I'm aware) is because 
the routine uses spin_lock/spin_unlock rather than the 
_irqsave/_irqrestore variants.  There's also a small efficiency issue: 
In the vast majority of cases involving real host controllers, the 
routine _will_ be called in interrupt context.  So we optimized for that 
case.

>  In the USB/IP code, however, it's called from the
> task context (see the stack trace below).
> 
> Is this something that is allowed and we need to fix kcov? Or is this
> a bug in USB/IP?

It's a bug in USB/IP.  Interrupts should be disabled when it calls 
usb_hcd_giveback_urb().

Alan Stern

  parent reply	other threads:[~2020-10-05 15:22 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-05 15:08 Is usb_hcd_giveback_urb() allowed in task context? Andrey Konovalov
2020-10-05 15:18 ` Greg Kroah-Hartman
2020-10-05 15:21   ` Andrey Konovalov
2020-10-05 15:25     ` Alan Stern
2020-10-05 23:38       ` Shuah Khan
2020-10-06  1:23         ` Alan Stern
2020-10-06 15:44           ` Andrey Konovalov
2020-10-05 15:22 ` Alan Stern [this message]
2020-10-05 15:28   ` Greg Kroah-Hartman

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