Patchwork [RFC,v2,04/29] PCI/MSI/pSeries: Make quota traversing and requesting race-safe

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Submitter Alexander Gordeev
Date Oct. 18, 2013, 5:12 p.m.
Message ID <663c95d5c7c6863f248886add511dab83f15dd18.1382103786.git.agordeev@redhat.com>
Download mbox | patch
Permalink /patch/284840/
State Superseded
Headers show

Comments

Alexander Gordeev - Oct. 18, 2013, 5:12 p.m.
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
---
 arch/powerpc/platforms/pseries/msi.c |   24 ++++++++++++++++++++++--
 1 files changed, 22 insertions(+), 2 deletions(-)
Tejun Heo - Nov. 20, 2013, 3:43 p.m.
Hello,

Sorry about the long delay.  Was traveling quite a bit.

On Fri, Oct 18, 2013 at 07:12:04PM +0200, Alexander Gordeev wrote:
> Signed-off-by: Alexander Gordeev <agordeev@redhat.com>

Please explain what the race condition in detail and how it gets fixed
by the patch.  This isn't a trivial change and non-trivial changes
especially stuff like race condition fixes definitely require detailed
explanation.

Thanks.

Patch

diff --git a/arch/powerpc/platforms/pseries/msi.c b/arch/powerpc/platforms/pseries/msi.c
index 009ec73..0e1d288 100644
--- a/arch/powerpc/platforms/pseries/msi.c
+++ b/arch/powerpc/platforms/pseries/msi.c
@@ -26,6 +26,8 @@  static int query_token, change_token;
 #define RTAS_CHANGE_MSIX_FN	4
 #define RTAS_CHANGE_32MSI_FN	5
 
+static DEFINE_MUTEX(rtas_quota_mutex);
+
 /* RTAS Helpers */
 
 static int rtas_change_msi(struct pci_dn *pdn, u32 func, u32 num_irqs)
@@ -345,7 +347,9 @@  static int rtas_msi_check_device(struct pci_dev *pdev, int nvec, int type)
 	if (rc)
 		return rc;
 
+	mutex_lock(&rtas_quota_mutex);
 	quota = msi_quota_for_device(pdev, nvec);
+	mutex_unlock(&rtas_quota_mutex);
 
 	if (quota && quota < nvec)
 		return quota;
@@ -399,6 +403,7 @@  static int rtas_setup_msi_irqs(struct pci_dev *pdev, int nvec_in, int type)
 	struct msi_msg msg;
 	int nvec = nvec_in;
 	int use_32bit_msi_hack = 0;
+	int quota;
 
 	pdn = pci_get_pdn(pdev);
 	if (!pdn)
@@ -407,13 +412,21 @@  static int rtas_setup_msi_irqs(struct pci_dev *pdev, int nvec_in, int type)
 	if (type == PCI_CAP_ID_MSIX && check_msix_entries(pdev))
 		return -EINVAL;
 
+	mutex_lock(&rtas_quota_mutex);
+
+	quota = msi_quota_for_device(pdev, nvec);
+	if (quota && quota < nvec) {
+		mutex_unlock(&rtas_quota_mutex);
+		return quota;
+	}
+
 	/*
 	 * Firmware currently refuse any non power of two allocation
 	 * so we round up if the quota will allow it.
 	 */
 	if (type == PCI_CAP_ID_MSIX) {
 		int m = roundup_pow_of_two(nvec);
-		int quota = msi_quota_for_device(pdev, m);
+		quota = msi_quota_for_device(pdev, m);
 
 		if (quota >= m)
 			nvec = m;
@@ -433,8 +446,11 @@  again:
 				 * We only want to run the 32 bit MSI hack below if
 				 * the max bus speed is Gen2 speed
 				 */
-				if (pdev->bus->max_bus_speed != PCIE_SPEED_5_0GT)
+				if (pdev->bus->max_bus_speed !=
+				    PCIE_SPEED_5_0GT) {
+					mutex_unlock(&rtas_quota_mutex);
 					return rc;
+				}
 
 				use_32bit_msi_hack = 1;
 			}
@@ -459,6 +475,7 @@  again:
 			nvec = nvec_in;
 			goto again;
 		}
+		mutex_unlock(&rtas_quota_mutex);
 		pr_debug("rtas_msi: rtas_change_msi() failed\n");
 		return rc;
 	}
@@ -467,6 +484,7 @@  again:
 	list_for_each_entry(entry, &pdev->msi_list, list) {
 		hwirq = rtas_query_irq_number(pdn, i++);
 		if (hwirq < 0) {
+			mutex_unlock(&rtas_quota_mutex);
 			pr_debug("rtas_msi: error (%d) getting hwirq\n", hwirq);
 			return hwirq;
 		}
@@ -474,6 +492,7 @@  again:
 		virq = irq_create_mapping(NULL, hwirq);
 
 		if (virq == NO_IRQ) {
+			mutex_unlock(&rtas_quota_mutex);
 			pr_debug("rtas_msi: Failed mapping hwirq %d\n", hwirq);
 			return -ENOSPC;
 		}
@@ -486,6 +505,7 @@  again:
 		entry->msg = msg;
 	}
 
+	mutex_unlock(&rtas_quota_mutex);
 	return 0;
 }