[PATCH v3 0/3] s390/pci: Enable CONTEXT_ANALYSIS

[PATCH v3 0/3] s390/pci: Enable CONTEXT_ANALYSIS

[Heiko Carstens]

v3:

- Add Reviewed-by tags from Niklas to first and third patch and address
  nits [Niklas]

- Refactor second patch again to make it hopefully more readable [Niklas]

v2:

- Address potential zdev reference leak (false positive) by adding a
  comment, and moving get_zdev_by_fid() [Sashiko, Niklas]

- Note: this reveals a pre-existing bug: zpci_remove_reserved_devices()
  calls zpci_device_reserved() without holding locks. It looks like
  this can be fixed easily by adding a mutex_lock()/mutex_unlock()
  pair in zpci_remove_reserved_devices(), but that is not within
  the scope of this series, and up to the pci maintainers

v1:
Enable CONTEXT_ANALYSYS for s390's pci code.

Static code checking for acquiring and releasing locks used to be done
with sparse. That was removed with [1] and replaced with a clang based
approach [2]. The new approach requires that each subsystem needs to be
explicitly enabled for checking.

Do that for s390's pci code. In order to avoid false positives the code
has to be slightly reworked, since conditionally acquiring and releasing
locks does not work with the checker (besides that this is sub optimal
coding style).

[1] 5b63d0ae94cc ("compiler-context-analysis: Remove Sparse support")
[2] 3269701cb256 ("compiler-context-analysis: Add infrastructure for Context Analysis with Clang")

Heiko Carstens (3):
  s390/pci: Rework __zpci_event_error() to remove conditional locking
  s390/pci: Rework __zpci_event_availability() to remove conditional locking
  s390/pci: Enable CONTEXT_ANALYSIS

 arch/s390/pci/Makefile    |   2 +
 arch/s390/pci/pci_event.c | 205 ++++++++++++++++++++------------------
 2 files changed, 111 insertions(+), 96 deletions(-)

-- 
2.53.0

[PATCH v3 1/3] s390/pci: Rework __zpci_event_error() to remove conditional locking

[Heiko Carstens]

Clang's compiler based static context analysis does not work with
locks that are conditionally taken like in __zpci_event_error():

arch/s390/pci/pci_event.c:320:2: warning: mutex 'get_zdev_by_fid(ccdf->fid).state_lock'
 is not held on every path through here [-Wthread-safety-analysis]

Given that code which takes locks conditionally can be considered
suboptimal rework __zpci_event_error() to get rid of this.

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 arch/s390/pci/pci_event.c | 43 ++++++++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 19 deletions(-)

diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c
index 839bd91c056e..bead4ed5d4ab 100644
--- a/arch/s390/pci/pci_event.c
+++ b/arch/s390/pci/pci_event.c
@@ -288,6 +288,12 @@ static void zpci_event_io_failure(struct pci_dev *pdev, pci_channel_state_t es)
 	pci_dev_unlock(pdev);
 }
 
+static void __zpci_event_print_error(struct pci_dev *pdev, struct zpci_ccdf_err *ccdf)
+{
+	pr_err("%s: Event 0x%x reports an error for PCI function 0x%x\n",
+	       pdev ? pci_name(pdev) : "n/a", ccdf->pec, ccdf->fid);
+}
+
 static void __zpci_event_error(struct zpci_ccdf_err *ccdf)
 {
 	struct zpci_dev *zdev = get_zdev_by_fid(ccdf->fid);
@@ -301,24 +307,24 @@ static void __zpci_event_error(struct zpci_ccdf_err *ccdf)
 	zpci_err("error CCDF:\n");
 	zpci_err_hex(ccdf, sizeof(*ccdf));
 
-	if (zdev) {
-		mutex_lock(&zdev->state_lock);
-		rc = clp_refresh_fh(zdev->fid, &fh);
-		if (rc)
-			goto no_pdev;
-		if (!fh || ccdf->fh != fh) {
-			/* Ignore events with stale handles */
-			zpci_dbg(3, "err fid:%x, fh:%x (stale %x)\n",
-				 ccdf->fid, fh, ccdf->fh);
-			goto no_pdev;
-		}
-		zpci_update_fh(zdev, ccdf->fh);
-		if (zdev->zbus->bus)
-			pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);
-	}
+	if (!zdev)
+		return __zpci_event_print_error(NULL, ccdf);
 
-	pr_err("%s: Event 0x%x reports an error for PCI function 0x%x\n",
-	       pdev ? pci_name(pdev) : "n/a", ccdf->pec, ccdf->fid);
+	mutex_lock(&zdev->state_lock);
+	rc = clp_refresh_fh(zdev->fid, &fh);
+	if (rc)
+		goto no_pdev;
+	if (!fh || ccdf->fh != fh) {
+		/* Ignore events with stale handles */
+		zpci_dbg(3, "err fid:%x, fh:%x (stale %x)\n",
+			 ccdf->fid, fh, ccdf->fh);
+		goto no_pdev;
+	}
+	zpci_update_fh(zdev, ccdf->fh);
+	if (zdev->zbus->bus)
+		pdev = pci_get_slot(zdev->zbus->bus, zdev->devfn);
+
+	__zpci_event_print_error(pdev, ccdf);
 
 	if (!pdev)
 		goto no_pdev;
@@ -340,8 +346,7 @@ static void __zpci_event_error(struct zpci_ccdf_err *ccdf)
 	}
 	pci_dev_put(pdev);
 no_pdev:
-	if (zdev)
-		mutex_unlock(&zdev->state_lock);
+	mutex_unlock(&zdev->state_lock);
 	zpci_zdev_put(zdev);
 }
 
-- 
2.53.0

[PATCH v3 2/3] s390/pci: Rework __zpci_event_availability() to remove conditional locking

[Heiko Carstens]

Clang's compiler based static context analysis does not work with locks
that are conditionally taken like in __zpci_event_availability():

arch/s390/pci/pci_event.c:402:10: warning: mutex 'get_zdev_by_fid(ccdf->fid).state_lock'
  is not held on every path through here [-Wthread-safety-analysis]

Given that code which takes locks conditionally can be considered
suboptimal rework __zpci_event_availability() to get rid of this.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 arch/s390/pci/pci_event.c | 162 ++++++++++++++++++++------------------
 1 file changed, 85 insertions(+), 77 deletions(-)

diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c
index bead4ed5d4ab..0a9eecb62bd1 100644
--- a/arch/s390/pci/pci_event.c
+++ b/arch/s390/pci/pci_event.c
@@ -387,98 +387,106 @@ static void zpci_event_reappear(struct zpci_dev *zdev)
 	zpci_dbg(1, "rea fid:%x, fh:%x\n", zdev->fid, zdev->fh);
 }
 
-static void __zpci_event_availability(struct zpci_ccdf_avail *ccdf)
+static bool zpci_event_avail_any_device(struct zpci_ccdf_avail *ccdf)
 {
-	struct zpci_dev *zdev = get_zdev_by_fid(ccdf->fid);
-	bool existing_zdev = !!zdev;
-	enum zpci_state state;
+	/* 0x0306 - No handle or fid stored */
+	if (ccdf->pec != 0x0306)
+		return false;
+	/* 0x308 or 0x302 for multiple devices */
+	zpci_remove_reserved_devices();
+	zpci_scan_devices();
+	return true;
+}
 
-	zpci_dbg(3, "avl fid:%x, fh:%x, pec:%x\n",
-		 ccdf->fid, ccdf->fh, ccdf->pec);
-
-	if (existing_zdev)
-		mutex_lock(&zdev->state_lock);
+static void zpci_event_avail_new_device(struct zpci_ccdf_avail *ccdf)
+{
+	struct zpci_dev *zdev;
 
 	switch (ccdf->pec) {
 	case 0x0301: /* Reserved|Standby -> Configured */
-		if (!zdev) {
-			zdev = zpci_create_device(ccdf->fid, ccdf->fh, ZPCI_FN_STATE_CONFIGURED);
-			if (IS_ERR(zdev))
-				break;
-			if (zpci_add_device(zdev)) {
-				kfree(zdev);
-				break;
-			}
-		} else {
-			if (zdev->state == ZPCI_FN_STATE_RESERVED)
-				zpci_event_reappear(zdev);
-			/* the configuration request may be stale */
-			else if (zdev->state != ZPCI_FN_STATE_STANDBY)
-				break;
-			zdev->state = ZPCI_FN_STATE_CONFIGURED;
+		zdev = zpci_create_device(ccdf->fid, ccdf->fh, ZPCI_FN_STATE_CONFIGURED);
+		if (IS_ERR(zdev))
+			break;
+		if (zpci_add_device(zdev)) {
+			kfree(zdev);
+			break;
 		}
 		zpci_scan_configured_device(zdev, ccdf->fh);
 		break;
 	case 0x0302: /* Reserved -> Standby */
-		if (!zdev) {
-			zdev = zpci_create_device(ccdf->fid, ccdf->fh, ZPCI_FN_STATE_STANDBY);
-			if (IS_ERR(zdev))
-				break;
-			if (zpci_add_device(zdev)) {
-				kfree(zdev);
-				break;
-			}
-		} else {
-			if (zdev->state == ZPCI_FN_STATE_RESERVED)
-				zpci_event_reappear(zdev);
-			zpci_update_fh(zdev, ccdf->fh);
-		}
-		break;
-	case 0x0303: /* Deconfiguration requested */
-		if (zdev) {
-			/* The event may have been queued before we configured
-			 * the device.
-			 */
-			if (zdev->state != ZPCI_FN_STATE_CONFIGURED)
-				break;
-			zpci_update_fh(zdev, ccdf->fh);
-			zpci_deconfigure_device(zdev);
-		}
-		break;
-	case 0x0304: /* Configured -> Standby|Reserved */
-		if (zdev) {
-			/* The event may have been queued before we configured
-			 * the device.:
-			 */
-			if (zdev->state == ZPCI_FN_STATE_CONFIGURED)
-				zpci_event_hard_deconfigured(zdev, ccdf->fh);
-			/* The 0x0304 event may immediately reserve the device */
-			if (!clp_get_state(zdev->fid, &state) &&
-			    state == ZPCI_FN_STATE_RESERVED) {
-				zpci_device_reserved(zdev);
-			}
-		}
-		break;
-	case 0x0306: /* 0x308 or 0x302 for multiple devices */
-		zpci_remove_reserved_devices();
-		zpci_scan_devices();
-		break;
-	case 0x0308: /* Standby -> Reserved */
-		if (!zdev)
+		zdev = zpci_create_device(ccdf->fid, ccdf->fh, ZPCI_FN_STATE_STANDBY);
+		if (IS_ERR(zdev))
 			break;
-		zpci_device_reserved(zdev);
-		break;
-	default:
+		if (zpci_add_device(zdev)) {
+			kfree(zdev);
+			break;
+		}
 		break;
 	}
-	if (existing_zdev) {
-		mutex_unlock(&zdev->state_lock);
-		zpci_zdev_put(zdev);
+}
+
+static void zpci_event_avail_existing_device(struct zpci_dev *zdev, struct zpci_ccdf_avail *ccdf)
+{
+	enum zpci_state state;
+
+	switch (ccdf->pec) {
+	case 0x0301: /* Reserved|Standby -> Configured */
+		if (zdev->state == ZPCI_FN_STATE_RESERVED)
+			zpci_event_reappear(zdev);
+		/* the configuration request may be stale */
+		else if (zdev->state != ZPCI_FN_STATE_STANDBY)
+			break;
+		zdev->state = ZPCI_FN_STATE_CONFIGURED;
+		zpci_scan_configured_device(zdev, ccdf->fh);
+		break;
+	case 0x0302: /* Reserved -> Standby */
+		if (zdev->state == ZPCI_FN_STATE_RESERVED)
+			zpci_event_reappear(zdev);
+		zpci_update_fh(zdev, ccdf->fh);
+		break;
+	case 0x0303: /* Deconfiguration requested */
+		/* The event may have been queued before we configured
+		 * the device.
+		 */
+		if (zdev->state != ZPCI_FN_STATE_CONFIGURED)
+			break;
+		zpci_update_fh(zdev, ccdf->fh);
+		zpci_deconfigure_device(zdev);
+		break;
+	case 0x0304: /* Configured -> Standby|Reserved */
+		/* The event may have been queued before we configured
+		 * the device.:
+		 */
+		if (zdev->state == ZPCI_FN_STATE_CONFIGURED)
+			zpci_event_hard_deconfigured(zdev, ccdf->fh);
+		/* The 0x0304 event may immediately reserve the device */
+		if (!clp_get_state(zdev->fid, &state) &&
+		    state == ZPCI_FN_STATE_RESERVED) {
+			zpci_device_reserved(zdev);
+		}
+		break;
+	case 0x0308: /* Standby -> Reserved */
+		zpci_device_reserved(zdev);
+		break;
 	}
 }
 
 void zpci_event_availability(void *data)
 {
-	if (zpci_is_enabled())
-		__zpci_event_availability(data);
+	struct zpci_ccdf_avail *ccdf = data;
+	struct zpci_dev *zdev;
+
+	if (!zpci_is_enabled())
+		return;
+	zpci_dbg(3, "avl fid:%x, fh:%x, pec:%x\n",
+		 ccdf->fid, ccdf->fh, ccdf->pec);
+	if (zpci_event_avail_any_device(ccdf))
+		return;
+	zdev = get_zdev_by_fid(ccdf->fid);
+	if (!zdev)
+		return zpci_event_avail_new_device(ccdf);
+	mutex_lock(&zdev->state_lock);
+	zpci_event_avail_existing_device(zdev, ccdf);
+	mutex_unlock(&zdev->state_lock);
+	zpci_zdev_put(zdev);
 }
-- 
2.53.0

Re: [PATCH v3 2/3] s390/pci: Rework __zpci_event_availability() to remove conditional locking

[Niklas Schnelle]

On Wed, 2026-08-05 at 15:36 +0200, Heiko Carstens wrote:
> Clang's compiler based static context analysis does not work with locks
> that are conditionally taken like in __zpci_event_availability():
> 
> arch/s390/pci/pci_event.c:402:10: warning: mutex 'get_zdev_by_fid(ccdf->fid).state_lock'
>   is not held on every path through here [-Wthread-safety-analysis]
> 
> Given that code which takes locks conditionally can be considered
> suboptimal rework __zpci_event_availability() to get rid of this.
> 
> Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
> ---
>  arch/s390/pci/pci_event.c | 162 ++++++++++++++++++++------------------
>  1 file changed, 85 insertions(+), 77 deletions(-)
> 
> diff --git a/arch/s390/pci/pci_event.c b/arch/s390/pci/pci_event.c
> index bead4ed5d4ab..0a9eecb62bd1 100644
> --- a/arch/s390/pci/pci_event.c
> +++ b/arch/s390/pci/pci_event.c
--- snip ---
>  void zpci_event_availability(void *data)
>  {
> -	if (zpci_is_enabled())
> -		__zpci_event_availability(data);
> +	struct zpci_ccdf_avail *ccdf = data;
> +	struct zpci_dev *zdev;
> +
> +	if (!zpci_is_enabled())
> +		return;
> +	zpci_dbg(3, "avl fid:%x, fh:%x, pec:%x\n",
> +		 ccdf->fid, ccdf->fh, ccdf->pec);
> +	if (zpci_event_avail_any_device(ccdf))
> +		return;
> +	zdev = get_zdev_by_fid(ccdf->fid);
> +	if (!zdev)
> +		return zpci_event_avail_new_device(ccdf);
> +	mutex_lock(&zdev->state_lock);
> +	zpci_event_avail_existing_device(zdev, ccdf);
> +	mutex_unlock(&zdev->state_lock);
> +	zpci_zdev_put(zdev);
>  }

Thank you, this is exactly what I had in mind! And in my opinion
definitely much cleaner than even the original code.

Feel free to add:

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>

Thanks,
Niklas

[PATCH v3 3/3] s390/pci: Enable CONTEXT_ANALYSIS

[Heiko Carstens]

Enable CONTEXT_ANALYSIS since s390's pci code compiles now without
warnings.

Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
 arch/s390/pci/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/pci/Makefile b/arch/s390/pci/Makefile
index 1810e0944a4e..b8be1316491b 100644
--- a/arch/s390/pci/Makefile
+++ b/arch/s390/pci/Makefile
@@ -3,6 +3,8 @@
 # Makefile for the s390 PCI subsystem.
 #
 
+CONTEXT_ANALYSIS := y
+
 obj-$(CONFIG_PCI)	+= pci.o pci_irq.o pci_clp.o \
 			   pci_event.o pci_debug.o pci_insn.o pci_mmio.o \
 			   pci_bus.o pci_kvm_hook.o pci_report.o pci_fixup.o
-- 
2.53.0