linux-kernel - [RFC PATCH V3 08/26] vfio/pci: Move mutex acquisition into function

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Date:   Fri, 27 Oct 2023 10:00:40 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     jgg@...dia.com, yishaih@...dia.com,
        shameerali.kolothum.thodi@...wei.com, kevin.tian@...el.com,
        alex.williamson@...hat.com
Cc:     kvm@...r.kernel.org, dave.jiang@...el.com, jing2.liu@...el.com,
        ashok.raj@...el.com, fenghua.yu@...el.com,
        tom.zanussi@...ux.intel.com, reinette.chatre@...el.com,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: [RFC PATCH V3 08/26] vfio/pci: Move mutex acquisition into function

vfio_pci_set_irqs_ioctl() is the entrypoint for interrupt management
via the VFIO_DEVICE_SET_IRQS ioctl(). vfio_pci_set_irqs_ioctl() can
be called from a virtual device driver after its callbacks have been
configured to support the needed interrupt management.

The igate mutex is obtained before vfio_pci_set_irqs_ioctl() to protect
against concurrent changes to interrupt context. It should not be
necessary for all users of vfio_pci_set_irqs_ioctl() to remember to
take the mutex.

Acquire and release the mutex within vfio_pci_set_irqs_ioctl().

Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
---
Changes since RFC V2:
- Improve changelog.

 drivers/vfio/pci/vfio_pci_core.c  |  2 --
 drivers/vfio/pci/vfio_pci_intrs.c | 10 ++++++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index 5c9bd5d2db53..bf4de137ad2f 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1214,12 +1214,10 @@ static int vfio_pci_ioctl_set_irqs(struct vfio_pci_core_device *vdev,
 			return PTR_ERR(data);
 	}
 
-	mutex_lock(&vdev->intr_ctx.igate);
 
 	ret = vfio_pci_set_irqs_ioctl(&vdev->intr_ctx, hdr.flags, hdr.index,
 				      hdr.start, hdr.count, data);
 
-	mutex_unlock(&vdev->intr_ctx.igate);
 	kfree(data);
 
 	return ret;
diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
index a4c8b589c87b..5d600548b5d7 100644
--- a/drivers/vfio/pci/vfio_pci_intrs.c
+++ b/drivers/vfio/pci/vfio_pci_intrs.c
@@ -826,7 +826,9 @@ int vfio_pci_set_irqs_ioctl(struct vfio_pci_intr_ctx *intr_ctx, uint32_t flags,
 	int (*func)(struct vfio_pci_intr_ctx *intr_ctx, unsigned int index,
 		    unsigned int start, unsigned int count, uint32_t flags,
 		    void *data) = NULL;
+	int ret = -ENOTTY;
 
+	mutex_lock(&intr_ctx->igate);
 	switch (index) {
 	case VFIO_PCI_INTX_IRQ_INDEX:
 		switch (flags & VFIO_IRQ_SET_ACTION_TYPE_MASK) {
@@ -887,7 +889,11 @@ int vfio_pci_set_irqs_ioctl(struct vfio_pci_intr_ctx *intr_ctx, uint32_t flags,
 	}
 
 	if (!func)
-		return -ENOTTY;
+		goto out_unlock;
+
+	ret = func(intr_ctx, index, start, count, flags, data);
 
-	return func(intr_ctx, index, start, count, flags, data);
+out_unlock:
+	mutex_unlock(&intr_ctx->igate);
+	return ret;
 }
-- 
2.34.1