memory leak in rds_send_probe

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    c6dd78fc Merge branch 'x86-urgent-for-linus' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14be98c8600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8de7d700ea5ac607
dashboard link: https://syzkaller.appspot.com/bug?extid=5134cdf021c4ed5aaa5f
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=145df0c8600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=170001f4600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+5134cdf021c4ed5aaa5f@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: memory leak
unreferenced object 0xffff8881234e9c00 (size 512):
  comm "kworker/u4:2", pid 286, jiffies 4294948041 (age 7.750s)
  hex dump (first 32 bytes):
    01 00 00 00 00 00 00 00 08 9c 4e 23 81 88 ff ff  ..........N#....
    08 9c 4e 23 81 88 ff ff 18 9c 4e 23 81 88 ff ff  ..N#......N#....
  backtrace:
    [<0000000032e378fa>] kmemleak_alloc_recursive  
/./include/linux/kmemleak.h:43 [inline]
    [<0000000032e378fa>] slab_post_alloc_hook /mm/slab.h:522 [inline]
    [<0000000032e378fa>] slab_alloc /mm/slab.c:3319 [inline]
    [<0000000032e378fa>] __do_kmalloc /mm/slab.c:3653 [inline]
    [<0000000032e378fa>] __kmalloc+0x16d/0x2d0 /mm/slab.c:3664
    [<0000000015bc9536>] kmalloc /./include/linux/slab.h:557 [inline]
    [<0000000015bc9536>] kzalloc /./include/linux/slab.h:748 [inline]
    [<0000000015bc9536>] rds_message_alloc+0x3e/0xc0 /net/rds/message.c:291
    [<00000000a806d18d>] rds_send_probe.constprop.0+0x42/0x2f0  
/net/rds/send.c:1419
    [<00000000794a00cc>] rds_send_pong+0x1e/0x23 /net/rds/send.c:1482
    [<00000000b2a248d0>] rds_recv_incoming+0x27e/0x460 /net/rds/recv.c:343
    [<00000000ea1503db>] rds_loop_xmit+0x86/0x100 /net/rds/loop.c:96
    [<00000000a9857f5a>] rds_send_xmit+0x524/0x9a0 /net/rds/send.c:355
    [<00000000557b0101>] rds_send_worker+0x3c/0xd0 /net/rds/threads.c:200
    [<000000004ba94868>] process_one_work+0x23f/0x490  
/kernel/workqueue.c:2269
    [<00000000e793f811>] worker_thread+0x195/0x580 /kernel/workqueue.c:2415
    [<000000003ee8c1a1>] kthread+0x13e/0x160 /kernel/kthread.c:255
    [<000000004cd53c81>] ret_from_fork+0x1f/0x30  
/arch/x86/entry/entry_64.S:352



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