linux-kernel - Re: [PATCH] pci: Fix a possible sleep-in-atomic bug in pci_set_power

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Message-ID: <20171009081747.GA23371@kroah.com>
Date:   Mon, 9 Oct 2017 10:17:47 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Jia-Ju Bai <baijiaju1990@....com>
Cc:     patrik.r.jakobsson@...il.com, airlied@...ux.ie,
        bhelgaas@...gle.com, forest@...ttletooquiet.net, simon@...anor.nu,
        scott@...heina.com, tvboxspy@...il.com, dan.a.cashman@...il.com,
        golubev.mikhail@...il.com, devel@...verdev.osuosl.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] pci: Fix a possible sleep-in-atomic bug in
 pci_set_power_state

On Mon, Oct 09, 2017 at 04:16:20PM +0800, Jia-Ju Bai wrote:
> The drivers vt6655 and gma500 call pci_set_power_state under a spinlock, which may sleep.
> The function call paths are:
> gma_power_begin (acquire the spinlock) (drivers/gpu/drm/gma500/power.c)
>   gma_resume_pci
>     pci_set_power_state
>       __pci_start_power_transition (drivers/pci/pci.c)
>         msleep --> may sleep
> 
> gma_power_begin (acquire the spinlock) (drivers/gpu/drm/gma500/power.c)
>   gma_resume_pci
>     pci_enable_device
>       pci_enable_device_flags (drivers/pci/pci.c)
>         do_pci_enable_device
>           pci_set_power_state
>             __pci_start_power_transition
>               msleep --> may sleep
> 
> vt6655_suspend (acquire the spinlock) (drivers/staging/vt6655/device_main.c)
>   pci_set_power_state
>     __pci_start_power_transition (drivers/pci/pci.c)
>       msleep --> may sleep
> 
> To fix these bugs, msleep is replaced with mdelay in __pci_start_power_transition
> 
> These bugs are found by my static analysis tool and my code review.

Wait, no, why not fix the callers to not have a spinlock.  Those are the
only users of these calls that are doing so incorrectly, don't change
the PCI core for the fault of 2 broken drivers.

thanks,

greg k-h