io_uring: fix memleak in io_init_wq_offload()

In the Linux kernel, the following vulnerability has been resolved:

io_uring: fix memleak in io_init_wq_offload()

I got memory leak report when doing fuzz test:

BUG: memory leak

unreferenced object 0xffff888107310a80 (size 96):

comm "syz-executor.6", pid 4610, jiffies 4295140240 (age 20.135s)

hex dump (first 32 bytes):

01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

00 00 00 00 ad 4e ad de ff ff ff ff 00 00 00 00 .....N..........

backtrace:

[<000000001974933b>] kmalloc include/linux/slab.h:591 [inline]

[<000000001974933b>] kzalloc include/linux/slab.h:721 [inline]

[<000000001974933b>] io_init_wq_offload fs/io_uring.c:7920 [inline]

[<000000001974933b>] io_uring_alloc_task_context+0x466/0x640 fs/io_uring.c:7955

[<0000000039d0800d>] __io_uring_add_tctx_node+0x256/0x360 fs/io_uring.c:9016

[<000000008482e78c>] io_uring_add_tctx_node fs/io_uring.c:9052 [inline]

[<000000008482e78c>] __do_sys_io_uring_enter fs/io_uring.c:9354 [inline]

[<000000008482e78c>] __se_sys_io_uring_enter fs/io_uring.c:9301 [inline]

[<000000008482e78c>] __x64_sys_io_uring_enter+0xabc/0xc20 fs/io_uring.c:9301

[<00000000b875f18f>] do_syscall_x64 arch/x86/entry/common.c:50 [inline]

[<00000000b875f18f>] do_syscall_64+0x3b/0x90 arch/x86/entry/common.c:80

[<000000006b0a8484>] entry_SYSCALL_64_after_hwframe+0x44/0xae

CPU0 CPU1

io_uring_enter io_uring_enter

io_uring_add_tctx_node io_uring_add_tctx_node

__io_uring_add_tctx_node __io_uring_add_tctx_node

io_uring_alloc_task_context io_uring_alloc_task_context

io_init_wq_offload io_init_wq_offload

hash = kzalloc hash = kzalloc

ctx->hash_map = hash ctx->hash_map = hash <- one of the hash is leaked

When calling io_uring_enter() in parallel, the 'hash_map' will be leaked,

add uring_lock to protect 'hash_map'.