diff mbox series

[1/9] driver core: rely on put_device to free dev->p

Message ID 20260902170734.95504-2-djeffery@redhat.com
State New
Headers show
Series shut down devices asynchronously | expand

Commit Message

David Jeffery Sept. 2, 2026, 5:07 p.m. UTC 
From: Tarun Sahu <tarunsahu@google.com>

device_add allocate private_data for device and assigns to
dev->p. If device_add fails in later steps of the function,
it cleans up this dev->p which is not necessary because In
the next call, put_device free it anyway (if reference to
the device is 0 which will be unless someone concurrently
get the reference to this device).

This avoids unnecessary races introduced in system. After device
is added in device_kset->list by device_add and later steps in the
device_add function failures occur, it will free dev->p manually,
while in between there might be a user of device_kset->list will
take reference to the device just added by device_add. and might
try to access dev->p. So relying on put_device to free dev->p
prevents such problem.

Signed-off-by: Tarun Sahu <tarunsahu@google.com>
Signed-off-by: David Jeffery <djeffery@redhat.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
---
 drivers/base/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

Comments

sashiko-bot@kernel.org Sept. 2, 2026, 5:16 p.m. UTC | #1 
> From: Tarun Sahu <tarunsahu@google.com>
> 
> device_add allocate private_data for device and assigns to
> dev->p. If device_add fails in later steps of the function,
> it cleans up this dev->p which is not necessary because In
> the next call, put_device free it anyway (if reference to
> the device is 0 which will be unless someone concurrently
> get the reference to this device).
> 
> This avoids unnecessary races introduced in system. After device
> is added in device_kset->list by device_add and later steps in the
> device_add function failures occur, it will free dev->p manually,
> while in between there might be a user of device_kset->list will
> take reference to the device just added by device_add. and might
> try to access dev->p. So relying on put_device to free dev->p
> prevents such problem.
> 
> Signed-off-by: Tarun Sahu <tarunsahu@google.com>
> Signed-off-by: David Jeffery <djeffery@redhat.com>

Sashiko has reviewed this patch and found no issues. It looks great!
diff mbox series

Patch

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 4c0c373998a1..83263e3fa5d4 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -2618,6 +2618,7 @@  static void device_release(struct kobject *kobj)
 	struct device *dev = kobj_to_dev(kobj);
 	struct device_private *p = dev->p;
 
+	dev->p = NULL;
 	/*
 	 * Some platform devices are driven without driver attached
 	 * and managed resources may have been acquired.  Make sure
@@ -3828,8 +3829,6 @@  int device_add(struct device *dev)
 parent_error:
 	put_device(parent);
 name_error:
-	kfree(dev->p);
-	dev->p = NULL;
 	goto done;
 }
 EXPORT_SYMBOL_GPL(device_add);