fpga: Fix memory leak for fpga_region_test_class_find()

fpga_region_class_find() in fpga_region_test_class_find() will call
get_device() if the data is matched, which will increment refcount for
dev->kobj, so it should call put_device() to decrement refcount for
dev->kobj to free the region, because fpga_region_unregister() will call
fpga_region_dev_release() only when the refcount for dev->kobj is zero
but fpga_region_test_init() call device_register() in
fpga_region_register_full(), which also increment refcount.

So call put_device() after calling fpga_region_class_find() in
fpga_region_test_class_find(). After applying this patch, the following
memory leak is never detected.

unreferenced object 0xffff88810c8ef000 (size 1024):
  comm "kunit_try_catch", pid 1875, jiffies 4294715298 (age 836.836s)
  hex dump (first 32 bytes):
    b8 d1 fb 05 81 88 ff ff 08 f0 8e 0c 81 88 ff ff  ................
    08 f0 8e 0c 81 88 ff ff 00 00 00 00 00 00 00 00  ................
  backtrace:
    [<ffffffff817ebad7>] kmalloc_trace+0x27/0xa0
    [<ffffffffa02385e1>] fpga_region_register_full+0x51/0x430 [fpga_region]
    [<ffffffffa0228e47>] 0xffffffffa0228e47
    [<ffffffff829c479d>] kunit_try_run_case+0xdd/0x250
    [<ffffffff829c9f2a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
    [<ffffffff81238b85>] kthread+0x2b5/0x380
    [<ffffffff81097ded>] ret_from_fork+0x2d/0x70
    [<ffffffff810034d1>] ret_from_fork_asm+0x11/0x20
unreferenced object 0xffff888105fbd1b8 (size 8):
  comm "kunit_try_catch", pid 1875, jiffies 4294715298 (age 836.836s)
  hex dump (first 8 bytes):
    72 65 67 69 6f 6e 30 00                          region0.
  backtrace:
    [<ffffffff817ec023>] __kmalloc_node_track_caller+0x53/0x150
    [<ffffffff82995590>] kvasprintf+0xb0/0x130
    [<ffffffff83f713b1>] kobject_set_name_vargs+0x41/0x110
    [<ffffffff8304ac1b>] dev_set_name+0xab/0xe0
    [<ffffffffa02388a2>] fpga_region_register_full+0x312/0x430 [fpga_region]
    [<ffffffffa0228e47>] 0xffffffffa0228e47
    [<ffffffff829c479d>] kunit_try_run_case+0xdd/0x250
    [<ffffffff829c9f2a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
    [<ffffffff81238b85>] kthread+0x2b5/0x380
    [<ffffffff81097ded>] ret_from_fork+0x2d/0x70
    [<ffffffff810034d1>] ret_from_fork_asm+0x11/0x20
unreferenced object 0xffff88810b3b8a00 (size 256):
  comm "kunit_try_catch", pid 1875, jiffies 4294715298 (age 836.836s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 08 8a 3b 0b 81 88 ff ff  ..........;.....
    08 8a 3b 0b 81 88 ff ff e0 ac 04 83 ff ff ff ff  ..;.............
  backtrace:
    [<ffffffff817ebad7>] kmalloc_trace+0x27/0xa0
    [<ffffffff83056d7a>] device_add+0xa2a/0x15e0
    [<ffffffffa02388b1>] fpga_region_register_full+0x321/0x430 [fpga_region]
    [<ffffffffa0228e47>] 0xffffffffa0228e47
    [<ffffffff829c479d>] kunit_try_run_case+0xdd/0x250
    [<ffffffff829c9f2a>] kunit_generic_run_threadfn_adapter+0x4a/0x90
    [<ffffffff81238b85>] kthread+0x2b5/0x380
    [<ffffffff81097ded>] ret_from_fork+0x2d/0x70
    [<ffffffff810034d1>] ret_from_fork_asm+0x11/0x20

Fixes: 64a5f97 ("fpga: add an initial KUnit suite for the FPGA Region")
Signed-off-by: Jinjie Ruan <[email protected]>
Reviewed-by: Marco Pagani <[email protected]>
Acked-by: Xu Yilun <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[[email protected]: slightly changes the commit message]
Signed-off-by: Xu Yilun <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Jinjie Ruan

drivers/fpga/tests/fpga-region-test.c

@@ -93,6 +93,8 @@ static void fpga_region_test_class_find(struct kunit *test)
 
 	region = fpga_region_class_find(NULL, &ctx->region_pdev->dev, fake_region_match);
 	KUNIT_EXPECT_PTR_EQ(test, region, ctx->region);
+
+	put_device(&region->dev);
 }
 
 /*