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    SubjectRe: [PATCH] pci_get_device call from interrupt in reboot fixups
    Andrew Morton wrote:
    > On Mon, 6 Aug 2007 19:49:10 -0700 Greg KH <> wrote:
    >> On Mon, Aug 06, 2007 at 11:16:20AM +0400, Denis V. Lunev wrote:
    >>> Greg KH wrote:
    >>>> On Fri, Aug 03, 2007 at 02:39:24PM +0400, Denis V. Lunev wrote:
    >>>>> The following calltrace is possible now:
    >>>>> handle_sysrq
    >>>>> machine_emergency_restart
    >>>>> mach_reboot_fixups
    >>>>> pci_get_device
    >>>>> pci_get_subsys
    >>>>> down_read
    >>>>> The patch obtains PCI device during initialization to avoid bothering PCI
    >>>>> search engine in interrupt. Devices used in this code are not supposed to
    >>>>> be pluggable, so it looks safe to keep them.
    >>>> What devices are supposed to be affected here? Are you sure that they
    >>>> can't be removed later? Grabbing references here might mess with them
    >>>> in the future.
    >>> Right now the list is the following:
    >>> static struct device_fixup fixups_table[] = {
    >>> cs5530a_warm_reset },
    >>> { PCI_VENDOR_ID_AMD, PCI_DEVICE_ID_AMD_CS5536_ISA, cs5536_warm_reset },
    >>> };
    >>> Though, if the approach is not suitable, we can skip fixups if we came
    >>> from sysrq.
    >> I don't think we really need to do fixups when we are "crashing" like
    >> this. The user really isn't shutting down the kernel as it should
    >> normally do.
    >> Andrew, I really don't want to change the PCI core to handle this, as we
    >> finally fixed a lot of issues with drivers trying to walk these lists
    >> from interrupt context. So if you want to just hide the warning message
    >> as we are shutting down, that's fine with me. Or just don't do the
    >> fixups. But grabbing a reference to the pci device is unsafe in my
    >> opinion and I do not want to do that.
    > OK, good decision ;)
    > One approach would be for some brave soul to pick his way through
    > the reboot code and ensure that we are correctly and reliably setting
    > system_state to SYSTEM_RESTART, then test that in __might_sleep().
    > But this does suppress somewhat-useful debugging just because of sysrq-B
    > and I really wouldn't want to utilise the horrid system_state any more that
    > we are presently doing. I think on balance that it would be better if we
    > could do something more targetted, like modify emergency_restart() to test
    > in_interrupt() and to then apologetically set some well-named global flag
    > which will shut up __might_sleep(). Pretty foul, but I can't think of
    > anything better.

    __might_sleep prevention will solve the problem only partially :( There
    is a direct WARN_ON(in_interrupt()) in pci_get_subsys.

    IMHO, calling down_read(&pci_bus_sem); from sysrq-B is not an option.
    I'll send a fixup disabling patch in a moment.
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      Last update: 2007-08-07 09:51    [W:0.046 / U:61.432 seconds]
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