[PATCH 2/2] firewire: core: use lock in Xarray instead of local R/W semaphore

From: Takashi Sakamoto
Date: Sun Aug 11 2024 - 21:43:16 EST


The data of XArray structure includes spinlock and requires no external
lock, while the data is still under the critical section by
fw_device_rwsem.

This commit deletes the critical section.

Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
---
drivers/firewire/core-device.c | 19 ++++++-------------
1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index 9f3276aa463a..32ac0f115793 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -806,7 +806,6 @@ static int shutdown_unit(struct device *device, void *data)

/*
* fw_device_rwsem acts as dual purpose mutex:
- * - serializes accesses to fw_device_idr,
* - serializes accesses to fw_device.config_rom/.config_rom_length and
* fw_unit.directory, unless those accesses happen at safe occasions
*/
@@ -819,8 +818,6 @@ struct fw_device *fw_device_get_by_devt(dev_t devt)
{
struct fw_device *device;

- guard(rwsem_read)(&fw_device_rwsem);
-
device = xa_load(&fw_device_xa, MINOR(devt));
if (device)
fw_device_get(device);
@@ -874,8 +871,7 @@ static void fw_device_shutdown(struct work_struct *work)
device_for_each_child(&device->device, NULL, shutdown_unit);
device_unregister(&device->device);

- scoped_guard(rwsem_write, &fw_device_rwsem)
- xa_erase(&fw_device_xa, MINOR(device->device.devt));
+ xa_erase(&fw_device_xa, MINOR(device->device.devt));

fw_device_put(device);
}
@@ -1087,12 +1083,10 @@ static void fw_device_init(struct work_struct *work)

fw_device_get(device);

- scoped_guard(rwsem_write, &fw_device_rwsem) {
- // The index of allocated entry is used for minor identifier of device node.
- ret = xa_alloc(&fw_device_xa, &minor, device, XA_LIMIT(0, MINORMASK), GFP_KERNEL);
- if (ret < 0)
- goto error;
- }
+ // The index of allocated entry is used for minor identifier of device node.
+ ret = xa_alloc(&fw_device_xa, &minor, device, XA_LIMIT(0, MINORMASK), GFP_KERNEL);
+ if (ret < 0)
+ goto error;

device->device.bus = &fw_bus_type;
device->device.type = &fw_device_type;
@@ -1152,8 +1146,7 @@ static void fw_device_init(struct work_struct *work)
return;

error_with_cdev:
- scoped_guard(rwsem_write, &fw_device_rwsem)
- xa_erase(&fw_device_xa, minor);
+ xa_erase(&fw_device_xa, minor);
error:
fw_device_put(device); // fw_device_xa's reference.

--
2.43.0