linux-kernel - Re: [PATCH v2] usb: host: oxu210hp-hcd: Fix potential deadlock on &oxu->mem

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Date:   Tue, 8 Aug 2023 10:28:14 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Chengfeng Ye <dg573847474@...il.com>
Cc:     gustavoars@...nel.org, u.kleine-koenig@...gutronix.de,
        giometti@...ux.it, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] usb: host: oxu210hp-hcd: Fix potential deadlock on
 &oxu->mem_lock

On Sat, Jul 29, 2023 at 09:26:34AM +0000, Chengfeng Ye wrote:
> &oxu->mem_lock is acquired by isr oxu_irq() along the below call
> chain under hardirq context.
> 
> <hard interrupt>
>         -> oxu_irq()
>         -> oxu210_hcd_irq()
>         -> ehci_work()
>         -> scan_async()
>         -> qh_completions()
>         -> oxu_murb_free()
>         -> spin_lock(&oxu->mem_lock)
> 
> Thus the acquisition of the lock under process context should disable
> irq, otherwise deadlock could happen if the irq happens to preempt the
> execution while the lock is held in process context on the same CPU.
> 
> This flaw was found by an experimental static analysis tool I am developing
> for irq-related deadlock. x86_64 allmodconfig using gcc shows no new
> warning.
> 
> The patch fixes the potential deadlocks by using spin_lock_irqsave() on
> &oxu->mem_lock
> 
> Signed-off-by: Chengfeng Ye <dg573847474@...il.com>
> 
> Changes in v2
> - use spin_lock_irqsave() on more potential deadlock sites of &oxu->mem_lock

This needs to be below the --- line, as documented, so it doesn't show
up in the changelog.

How did you test this change?  Do you have hardware to test it out?  If
not, I don't think we can accpet this, see the kernel documentation for
what we accept from tools and researchers.

thanks,

greg k-h