linux-kernel - [PATCH] pci: avoid bridge feature re-probing on hotplug

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Message-ID: <20181211021617.24072-1-mst@redhat.com>
Date:   Mon, 10 Dec 2018 21:18:40 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     xuyandong <xuyandong2@...wei.com>, stable@...r.kernel.org,
        Yinghai Lu <yinghai@...nel.org>,
        Jesse Barnes <jbarnes@...tuousgeek.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: [PATCH] pci: avoid bridge feature re-probing on hotplug

commit 1f82de10d6 ("PCI/x86: don't assume prefetchable ranges are
64bit") added probing of bridge support for 64 bit memory
each time bridge is re-enumerated.

Unfortunately this probing is destructive if any device behind
the bridge is in use at this time.

There's no real need to re-probe the bridge features as the
regiters in question never change - detect that using
the memory flag being set and skip the probing.
Avoiding repeated calls to pci_bridge_check_ranges might be even nicer
would be a bigger patch and probably not appropriate on stable.

Reported-by: xuyandong <xuyandong2@...wei.com>
Cc: stable@...r.kernel.org
Cc: Yinghai Lu <yinghai@...nel.org>
Cc: Jesse Barnes <jbarnes@...tuousgeek.org>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---

This issue has been reported on upstream Linux and Centos.

 drivers/pci/setup-bus.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index ed960436df5e..7ab42f76579e 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -741,6 +741,13 @@ static void pci_bridge_check_ranges(struct pci_bus *bus)
 	struct resource *b_res;

 	b_res = &bridge->resource[PCI_BRIDGE_RESOURCES];
+
+	/* Don't re-check after this was called once already:
+	 * important since bridge might be in use.
+	 */
+	if (b_res[1].flags & IORESOURCE_MEM)
+		return;
+
 	b_res[1].flags |= IORESOURCE_MEM;

 	pci_read_config_word(bridge, PCI_IO_BASE, &io);
-- 
MST