workqueue, lockdep: Fix a memory leak in wq->lock_name

The following commit:

  669de8bd ("kernel/workqueue: Use dynamic lockdep keys for workqueues")

introduced a memory leak as wq_free_lockdep() calls kfree(wq->lock_name),
but wq_init_lockdep() does not point wq->lock_name to the newly allocated
slab object.

This can be reproduced by running LTP fallocate04 followed by oom01 tests:

 unreferenced object 0xc0000005876384d8 (size 64):
  comm "fallocate04", pid 26972, jiffies 4297139141 (age 40370.480s)
  hex dump (first 32 bytes):
    28 77 71 5f 63 6f 6d 70 6c 65 74 69 6f 6e 29 65  (wq_completion)e
    78 74 34 2d 72 73 76 2d 63 6f 6e 76 65 72 73 69  xt4-rsv-conversi
  backtrace:
    [<00000000cb452883>] kvasprintf+0x6c/0xe0
    [<000000004654ddac>] kasprintf+0x34/0x60
    [<000000001c68f311>] alloc_workqueue+0x1f8/0x6ac
    [<0000000003c2ad83>] ext4_fill_super+0x23d4/0x3c80 [ext4]
    [<0000000006610538>] mount_bdev+0x25c/0x290
    [<00000000bcf955ec>] ext4_mount+0x28/0x50 [ext4]
    [<0000000016e08fd3>] legacy_get_tree+0x4c/0xb0
    [<0000000042b6a5fc>] vfs_get_tree+0x6c/0x190
    [<00000000268ab022>] do_mount+0xb9c/0x1100
    [<00000000698e6898>] ksys_mount+0x158/0x180
    [<0000000064e391fd>] sys_mount+0x20/0x30
    [<00000000ba378f12>] system_call+0x5c/0x70
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: catalin.marinas@arm.com
Cc: jiangshanlai@gmail.com
Cc: tj@kernel.org
Fixes: 669de8bd ("kernel/workqueue: Use dynamic lockdep keys for workqueues")
Link: https://lkml.kernel.org/r/20190307002731.47371-1-cai@lca.pwSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/workqueue.c

@@ -3348,6 +3348,8 @@ static void wq_init_lockdep(struct workqueue_struct *wq)
 	lock_name = kasprintf(GFP_KERNEL, "%s%s", "(wq_completion)", wq->name);
 	if (!lock_name)
 		lock_name = wq->name;
+
+	wq->lock_name = lock_name;
 	lockdep_init_map(&wq->lockdep_map, lock_name, &wq->key, 0);
 }