Re: [syzbot] [block?] WARNING: suspicious RCU usage in mas_start (2)

Re: [syzbot] [block?] WARNING: suspicious RCU usage in mas_start (2)

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in io_wq_put_and_exit

------------[ cut here ]------------
time_after(jiffies, warn_timeout)
WARNING: io_uring/io-wq.c:1378 at io_wq_exit_workers io_uring/io-wq.c:1378 [inline], CPU#0: syz.0.29/6458
WARNING: io_uring/io-wq.c:1378 at io_wq_put_and_exit+0x736/0xaa0 io_uring/io-wq.c:1407, CPU#0: syz.0.29/6458
Modules linked in:
CPU: 0 UID: 0 PID: 6458 Comm: syz.0.29 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2026
RIP: 0010:io_wq_exit_workers io_uring/io-wq.c:1378 [inline]
RIP: 0010:io_wq_put_and_exit+0x736/0xaa0 io_uring/io-wq.c:1407
Code: 78 22 e8 5d 74 ee fc 4c 89 e7 4c 89 fe e8 a2 c4 0d 07 48 85 c0 75 18 e8 48 74 ee fc 80 3c 2b 00 75 bb eb c5 e8 3b 74 ee fc 90 <0f> 0b 90 eb d8 e8 30 74 ee fc 4c 8b 2c 24 4d 8d 7d 08 4c 89 fd 48
RSP: 0018:ffffc9000207f838 EFLAGS: 00010293
RAX: ffffffff84d967c5 RBX: 1ffffffff1d41e50 RCX: ffff88807d221f40
RDX: 0000000000000000 RSI: ffffffffffffe945 RDI: 0000000000000000
RBP: dffffc0000000000 R08: ffffffff907a517f R09: 1ffffffff20f4a2f
R10: dffffc0000000000 R11: fffffbfff20f4a30 R12: ffff888028864018
R13: 0000000100003546 R14: 0000000100004c01 R15: 0000000000001b58
FS:  00007fd861d256c0(0000) GS:ffff888124ccb000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055944da2bd51 CR3: 000000002b20a000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 io_uring_clean_tctx+0x12e/0x1b0 io_uring/tctx.c:258
 io_uring_cancel_generic+0x6c0/0x7d0 io_uring/cancel.c:655
 io_uring_files_cancel include/linux/io_uring.h:20 [inline]
 do_exit+0x39f/0x2360 kernel/exit.c:952
 do_group_exit+0x22d/0x2f0 kernel/exit.c:1155
 get_signal+0x121b/0x12c0 kernel/signal.c:3112
 arch_do_signal_or_restart+0xbb/0x860 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x10e/0x770 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x328/0x520 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd860d9e159
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd861d250e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007fd861025fa8 RCX: 00007fd860d9e159
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007fd861025fa8
RBP: 00007fd861025fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd861026038 R14: 00007fffbb02fd80 R15: 00007fffbb02fe68
 </TASK>


Tested on:

commit:         f0100363 Merge tag 'xfs-fixes-7.3-rc5' of gitolite.ker..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=1147745e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=9d4242cb1c54cdf7
dashboard link: https://syzkaller.appspot.com/bug?extid=b48868c46e62c1c4cb2c
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=114f3525580000

[syzbot] [block?] WARNING: suspicious RCU usage in mas_start (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    704340f1cd0d Merge tag 'x86_urgent_for_7.3-rc4' of git://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16091925580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5c3949d762a91f
dashboard link: https://syzkaller.appspot.com/bug?extid=b48868c46e62c1c4cb2c
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=120f305e580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=117fb5f9580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-704340f1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e02afc1c5927/vmlinux-704340f1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/09cb4a8b3309/bzImage-704340f1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b48868c46e62c1c4cb2c@syzkaller.appspotmail.com

=============================
WARNING: suspicious RCU usage
syzkaller #0 Not tainted
-----------------------------
lib/maple_tree.c:720 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
locks held by syz.0.17/5926: 1, last CPU#0:
 #0: ffff888034a420a0 (&ctx->uring_lock){+.+.}-{4:4}, at: tctx_task_work_run+0x1cd/0xbf0 io_uring/tw.c:92

stack backtrace:
CPU: 0 UID: 0 PID: 5926 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 lockdep_rcu_suspicious.cold+0x4f/0xb2 kernel/locking/lockdep.c:6972
 mas_root lib/maple_tree.c:720 [inline]
 mas_start+0x621/0x7c0 lib/maple_tree.c:1250
 mas_state_walk lib/maple_tree.c:3006 [inline]
 mas_walk+0x82/0x310 lib/maple_tree.c:4458
 ublk_try_buf_match+0x469/0x7e0 drivers/block/ublk_drv.c:5639
 ublk_init_iod+0x4a4/0x5b0 drivers/block/ublk_drv.c:521
 ublk_setup_iod+0x145/0x2f0 drivers/block/ublk_drv.c:1536
 ublk_dispatch_req+0x4e/0xb00 drivers/block/ublk_drv.c:1776
 ublk_cmd_tw_cb+0xbe/0x110 drivers/block/ublk_drv.c:2067
 tctx_task_work_run+0xabe/0xbf0 io_uring/tw.c:96
 tctx_task_work+0x7a/0xa0 io_uring/tw.c:133
 task_work_run+0x150/0x240 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x951/0x2ae0 kernel/exit.c:1011
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1154
 __do_sys_exit_group kernel/exit.c:1165 [inline]
 __se_sys_exit_group kernel/exit.c:1163 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1163
 x64_sys_call+0x1567/0x1570 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x123/0x790 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f35df99e159
Code: Unable to access opcode bytes at 0x7f35df99e12f.
RSP: 002b:00007ffcaa2c82b8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f35df99e159
RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000003 R08: 0000000000000000 R09: 00007f35dfbec3e0
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f35dfbec3e0 R14: 0000000000000003 R15: 00007ffcaa2c8370
 </TASK>
I/O error, dev ublkb0, sector 0 op 0x0:(READ) flags 0x800000 phys_seg 1 prio class 2
Buffer I/O error on dev ublkb0, logical block 0, async page read


---
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