nvme: fix memory leak caused by incorrect subsystem free

When freeing the subsystem after finding another match with
__nvme_find_get_subsystem(), use put_device() instead of
__nvme_release_subsystem() which calls kfree() directly.

Per the documentation, put_device() should always be used
after device_initialization() is called. Otherwise, leaks
like the one below which was detected by kmemleak may occur.

Once the call of __nvme_release_subsystem() is removed it no
longer makes sense to keep the helper, so fold it back
into nvme_release_subsystem().

unreferenced object 0xffff8883d12bfbc0 (size 16):
  comm "nvme", pid 2635, jiffies 4294933602 (age 739.952s)
  hex dump (first 16 bytes):
    6e 76 6d 65 2d 73 75 62 73 79 73 32 00 88 ff ff  nvme-subsys2....
  backtrace:
    [<000000007d8fc208>] __kmalloc_track_caller+0x16d/0x2a0
    [<0000000081169e5f>] kvasprintf+0xad/0x130
    [<0000000025626f25>] kvasprintf_const+0x47/0x120
    [<00000000fa66ad36>] kobject_set_name_vargs+0x44/0x120
    [<000000004881f8b3>] dev_set_name+0x98/0xc0
    [<000000007124dae3>] nvme_init_identify+0x1995/0x38e0
    [<000000009315020a>] nvme_loop_configure_admin_queue+0x4fa/0x5e0
    [<000000001a63e766>] nvme_loop_create_ctrl+0x489/0xf80
    [<00000000a46ecc23>] nvmf_dev_write+0x1a12/0x2220
    [<000000002259b3d5>] __vfs_write+0x66/0x120
    [<000000002f6df81e>] vfs_write+0x154/0x490
    [<000000007e8cfc19>] ksys_write+0x10a/0x240
    [<00000000ff5c7b85>] __x64_sys_write+0x73/0xb0
    [<00000000fee6d692>] do_syscall_64+0xaa/0x470
    [<00000000997e1ede>] entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fixes: ab9e00cc72 ("nvme: track subsystems")
Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -2311,15 +2311,13 @@ static void nvme_init_subnqn(struct nvme_subsystem *subsys, struct nvme_ctrl *ct
 	memset(subsys->subnqn + off, 0, sizeof(subsys->subnqn) - off);
 }
 
-static void __nvme_release_subsystem(struct nvme_subsystem *subsys)
-{
-	ida_simple_remove(&nvme_subsystems_ida, subsys->instance);
-	kfree(subsys);
-}
-
 static void nvme_release_subsystem(struct device *dev)
 {
-	__nvme_release_subsystem(container_of(dev, struct nvme_subsystem, dev));
+	struct nvme_subsystem *subsys =
+		container_of(dev, struct nvme_subsystem, dev);
+
+	ida_simple_remove(&nvme_subsystems_ida, subsys->instance);
+	kfree(subsys);
 }
 
 static void nvme_destroy_subsystem(struct kref *ref)
@@ -2477,7 +2475,7 @@ static int nvme_init_subsystem(struct nvme_ctrl *ctrl, struct nvme_id_ctrl *id)
 	mutex_lock(&nvme_subsystems_lock);
 	found = __nvme_find_get_subsystem(subsys->subnqn);
 	if (found) {
-		__nvme_release_subsystem(subsys);
+		put_device(&subsys->dev);
 		subsys = found;
 
 		if (!nvme_validate_cntlid(subsys, ctrl, id)) {