cxl: Change contexts_lock to a mutex to fix sleep while atomic bug

We had a known sleep while atomic bug if a CXL device was forcefully
unbound while it was in use. This could occur as a result of EEH, or
manually induced with something like this while the device was in use:

echo 0000:01:00.0 > /sys/bus/pci/drivers/cxl-pci/unbind

The issue was that in this code path we iterated over each context and
forcefully detached it with the contexts_lock spin lock held, however
the detach also needed to take the spu_mutex, and call schedule.

This patch changes the contexts_lock to a mutex so that we are not in
atomic context while doing the detach, thereby avoiding the sleep while
atomic.

Also delete the related TODO comment, which suggested an alternate
solution which turned out to not be workable.

Cc: stable@vger.kernel.org
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 5 insertions, 5 deletions

diff --git a/drivers/misc/cxl/sysfs.c b/drivers/misc/cxl/sysfs.c
index ce7ec06d87d1..461bdbd5d483 100644
--- a/drivers/misc/cxl/sysfs.c
+++ b/drivers/misc/cxl/sysfs.c
@@ -121,7 +121,7 @@ static ssize_t reset_store_afu(struct device *device,
 	int rc;
 
 	/* Not safe to reset if it is currently in use */
-	spin_lock(&afu->contexts_lock);
+	mutex_lock(&afu->contexts_lock);
 	if (!idr_is_empty(&afu->contexts_idr)) {
 		rc = -EBUSY;
 		goto err;
@@ -132,7 +132,7 @@ static ssize_t reset_store_afu(struct device *device,
 
 	rc = count;
 err:
-	spin_unlock(&afu->contexts_lock);
+	mutex_unlock(&afu->contexts_lock);
 	return rc;
 }
 
@@ -247,7 +247,7 @@ static ssize_t mode_store(struct device *device, struct device_attribute *attr,
 	int rc = -EBUSY;
 
 	/* can't change this if we have a user */
-	spin_lock(&afu->contexts_lock);
+	mutex_lock(&afu->contexts_lock);
 	if (!idr_is_empty(&afu->contexts_idr))
 		goto err;
 
@@ -271,7 +271,7 @@ static ssize_t mode_store(struct device *device, struct device_attribute *attr,
 	afu->current_mode = 0;
 	afu->num_procs = 0;
 
-	spin_unlock(&afu->contexts_lock);
+	mutex_unlock(&afu->contexts_lock);
 
 	if ((rc = _cxl_afu_deactivate_mode(afu, old_mode)))
 		return rc;
@@ -280,7 +280,7 @@ static ssize_t mode_store(struct device *device, struct device_attribute *attr,
 
 	return count;
 err:
-	spin_unlock(&afu->contexts_lock);
+	mutex_unlock(&afu->contexts_lock);
 	return rc;
 }