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    SubjectRe: [PATCH] PCI: hv: Fix a __local_bh_enable_ip warning in hv_compose_msi_msg()
    On Wed, Jun 13, 2018 at 08:32:13PM +0000, Dexuan Cui wrote:
    > > From: Dexuan Cui
    > > Sent: Wednesday, June 6, 2018 17:15
    > > To: Haiyang Zhang <haiyangz@microsoft.com>; Lorenzo Pieralisi
    > > <lorenzo.pieralisi@arm.com>; Bjorn Helgaas <bhelgaas@google.com>;
    > > linux-pci@vger.kernel.org; KY Srinivasan <kys@microsoft.com>; Stephen
    > > Hemminger <sthemmin@microsoft.com>; olaf@aepfle.de;
    > > apw@canonical.com; jasowang@redhat.com
    > > Cc: linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org;
    > > vkuznets@redhat.com; marcelo.cerri@canonical.com
    > > Subject: RE: [PATCH] PCI: hv: Fix a __local_bh_enable_ip warning in
    > > hv_compose_msi_msg()
    > >
    > > > From: Haiyang Zhang
    > > > Sent: Friday, May 25, 2018 12:52
    > > > To: Dexuan Cui <decui@microsoft.com>; Lorenzo Pieralisi
    > > > <lorenzo.pieralisi@arm.com>; Bjorn Helgaas <bhelgaas@google.com>;
    > > > linux-pci@vger.kernel.org; KY Srinivasan <kys@microsoft.com>; Stephen
    > > > Hemminger <sthemmin@microsoft.com>; olaf@aepfle.de;
    > > > apw@canonical.com; jasowang@redhat.com
    > > > Cc: linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org;
    > > > vkuznets@redhat.com; marcelo.cerri@canonical.com
    > > > Subject: RE: [PATCH] PCI: hv: Fix a __local_bh_enable_ip warning in
    > > > hv_compose_msi_msg()
    > > >
    > > > > From: Dexuan Cui
    > > > > Sent: Tuesday, May 22, 2018 8:18 PM
    > > > > To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>; Bjorn Helgaas
    > > > > <bhelgaas@google.com>; linux-pci@vger.kernel.org; KY Srinivasan
    > > > > <kys@microsoft.com>; Stephen Hemminger <sthemmin@microsoft.com>;
    > > > > olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com
    > > > > Cc: linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org;
    > > > > Haiyang Zhang <haiyangz@microsoft.com>; vkuznets@redhat.com;
    > > > > marcelo.cerri@canonical.com
    > > > > Subject: [PATCH] PCI: hv: Fix a __local_bh_enable_ip warning in
    > > > > hv_compose_msi_msg()
    > > > >
    > > > >
    > > > > Commit de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in
    > > > hv_compose_msi_msg()")
    > > > > uses local_bh_disable()/enable(), because hv_pci_onchannelcallback() can
    > > > also
    > > > > run in tasklet context as the channel event callback.
    > > > >
    > > > > With CONFIG_PROVE_LOCKING=y in the latest mainline, or old kernels that
    > > > > don't have commit f71b74bca637 ("irq/softirqs: Use lockdep to assert IRQs
    > > > are
    > > > > disabled/enabled"), it turns out can we trigger a warning at the beginning
    > > of
    > > > > __local_bh_enable_ip(), because the upper layer irq code can call
    > > > > hv_compose_msi_msg() with local irqs disabled.
    > > > >
    > > > > Let's fix the warning by switching to local_irq_save()/restore(). This is not an
    > > > > issue because hv_pci_onchannelcallback() is not slow, and it not a hot path.
    > > > >
    > > > > Fixes: de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in
    > > hv_compose_msi_msg()")
    > > > > Signed-off-by: Dexuan Cui <decui@microsoft.com>
    > > > > Cc: <stable@vger.kernel.org>
    > > > > Cc: Stephen Hemminger <sthemmin@microsoft.com>
    > > > > Cc: K. Y. Srinivasan <kys@microsoft.com>
    > > > > ---
    > > >
    > > > Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
    > > >
    > > > Thanks you.
    > >
    > > Hi Lorenzo,
    > >
    > > Can I have your reply to this patch?
    > >
    > > -- Dexuan
    >
    > It looks Lorenzo's pci.git tree has not been updated for 3+ weeks.
    > I guess Lorenzo may be on vacation.
    >
    > @Bjorn, can this patch go through your tree?
    > Should I resubmit it?

    No need to resubmit it, Lorenzo has been out for a bit, but I'm sure
    he'll pick this up as he catches up.

    You might, however, fix the commit log:

    This is not an issue because hv_pci_onchannelcallback() is not slow,
    and it not a hot path.

    This has at least one typo (I think you mean "and *is* not a hot
    path").

    I also don't understand the sentence as a whole because the
    hv_pci_onchannelcallback() comment says it's called whenever the host
    sends a packet to this channel, and that *does* sound like a hot path.

    I also don't understand the "hv_pci_onchannelcallback() is not slow"
    part. In other words, you're saying hv_pci_onchannelcallback() is
    fast and it's not a hot path. And apparently this has something to do
    with the difference between local_bh_disable() and local_irq_save()?

    Bjorn

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