Re: [PATCH 0/2] mm: Two small fixes for recent syzbot reports

[Hillf Danton <hdanton@sina.com>]

On Mon, 13 Apr 2020 18:06:21 -0400 Qian Cai wrote:
> 
> BTW, I=E2=80=99ll be adding fuzzers to my daily linux-next routines =
> where it triggers this
> io_uring/scheduler bug almost immediately, so hopefully would buy syzbot =
> some
> time to resume on linux-next.
> 
> [67493.516737][T211750] BUG: unable to handle page fault for address: =
> ffffffffffffffe8
> [67493.557315][T211750] #PF: supervisor read access in kernel mode
> [67493.586726][T211750] #PF: error_code(0x0000) - not-present page
> [67493.614434][T211750] PGD f96e17067 P4D f96e17067 PUD f96e19067 PMD 0=20=
> 
> [67493.644846][T211750] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
> [67493.674127][T211750] CPU: 55 PID: 211750 Comm: trinity-c127 Tainted: =
> G    B        L    5.7.0-rc1-next-20200413 #4
> [67493.722516][T211750] Hardware name: HP ProLiant DL380 Gen9/ProLiant =
> DL380 Gen9, BIOS P89 04/12/2017
> [67493.764925][T211750] RIP: 0010:__wake_up_common+0x98/0x290
> __wake_up_common at kernel/sched/wait.c:87
> [67493.790675][T211750] Code: 40 4d 8d 78 e8 49 8d 7f 18 49 39 fd 0f 84 =
> 80 00 00 00 e8 6b bd 2b 00 49 8b 5f 18 45 31 e4 48 83 eb 18 4c 89 ff e8 =
> 08 bc 2b 00 <45> 8b 37 41 f6 c6 04 75 71 49 8d 7f 10 e8 46 bd 2b 00 49 =
> 8b 47 10
> [67493.881650][T211750] RSP: 0018:ffffc9000adbfaf0 EFLAGS: 00010046
> [67493.909854][T211750] RAX: 0000000000000000 RBX: ffffffffffffffe8 RCX: =
> ffffffffaa9636b8
> [67493.947131][T211750] RDX: 0000000000000003 RSI: dffffc0000000000 RDI: =
> ffffffffffffffe8
> [67493.983829][T211750] RBP: ffffc9000adbfb40 R08: fffffbfff582c5fd R09: =
> fffffbfff582c5fd
> [67494.020861][T211750] R10: ffffffffac162fe3 R11: fffffbfff582c5fc R12: =
> 0000000000000000
> [67494.059249][T211750] R13: ffff888ef82b0960 R14: ffffc9000adbfb80 R15: =
> ffffffffffffffe8
> [67494.099699][T211750] FS:  00007fdcba4c4740(0000) =
> GS:ffff889033780000(0000) knlGS:0000000000000000
> [67494.141858][T211750] CS:  0010 DS: 0000 ES: 0000 CR0: =
> 0000000080050033
> [67494.172660][T211750] CR2: ffffffffffffffe8 CR3: 0000000f776a0004 CR4: =
> 00000000001606e0
> [67494.209760][T211750] Call Trace:
> [67494.224720][T211750]  __wake_up_common_lock+0xea/0x150
> (inlined by) __wake_up_common_lock at kernel/sched/wait.c:124
> [67494.248753][T211750]  ? __wake_up_common+0x290/0x290
> [67494.272014][T211750]  ? lockdep_hardirqs_on+0x16/0x2c0
> [67494.296139][T211750]  __wake_up+0x13/0x20
> [67494.314946][T211750]  io_cqring_ev_posted+0x75/0xe0
> (inlined by) io_cqring_ev_posted at fs/io_uring.c:1160
> [67494.337726][T211750]  io_ring_ctx_wait_and_kill+0x1c0/0x2f0
> io_ring_ctx_wait_and_kill at fs/io_uring.c:7305
> [67494.363840][T211750]  io_uring_create+0xa8d/0x13b0
> [67494.386526][T211750]  ? io_req_defer_prep+0x990/0x990
> [67494.410119][T211750]  ? __kasan_check_write+0x14/0x20
> [67494.433646][T211750]  io_uring_setup+0xb8/0x130
> [67494.454870][T211750]  ? io_uring_create+0x13b0/0x13b0
> [67494.478342][T211750]  ? check_flags.part.28+0x220/0x220
> [67494.502947][T211750]  ? lockdep_hardirqs_on+0x16/0x2c0
> [67494.526965][T211750]  __x64_sys_io_uring_setup+0x31/0x40
> [67494.551820][T211750]  do_syscall_64+0xcc/0xaf0
> [67494.574829][T211750]  ? syscall_return_slowpath+0x580/0x580
> [67494.604591][T211750]  ? lockdep_hardirqs_off+0x1f/0x140
> [67494.628901][T211750]  ? entry_SYSCALL_64_after_hwframe+0x3e/0xb3
> [67494.657616][T211750]  ? trace_hardirqs_off_caller+0x3a/0x150
> [67494.683999][T211750]  ? trace_hardirqs_off_thunk+0x1a/0x1c
> [67494.709982][T211750]  entry_SYSCALL_64_after_hwframe+0x49/0xb3


See if it makes your fuzzers happy.

--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -934,6 +934,7 @@ static struct io_ring_ctx *io_ring_ctx_a
 	idr_init(&ctx->personality_idr);
 	mutex_init(&ctx->uring_lock);
 	init_waitqueue_head(&ctx->wait);
+	init_waitqueue_head(&ctx->sqo_wait);
 	spin_lock_init(&ctx->completion_lock);
 	INIT_LIST_HEAD(&ctx->poll_list);
 	INIT_LIST_HEAD(&ctx->defer_list);
@@ -6824,7 +6825,6 @@ static int io_sq_offload_start(struct io
 {
 	int ret;
 
-	init_waitqueue_head(&ctx->sqo_wait);
 	mmgrab(current->mm);
 	ctx->sqo_mm = current->mm;