[syzbot] [ext4?] INFO: task hung in ext4_read_bh

[syzbot <syzbot+18edb60ce92acd5b4674@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    7fa4d8dc380f Add linux-next specific files for 20250821
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16a46662580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ae76068823a236b3
dashboard link: https://syzkaller.appspot.com/bug?extid=18edb60ce92acd5b4674
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11a46662580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1399da62580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/63178c6ef3f8/disk-7fa4d8dc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c5c27b0841e0/vmlinux-7fa4d8dc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9a8832715cca/bzImage-7fa4d8dc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+18edb60ce92acd5b4674@syzkaller.appspotmail.com

INFO: task syz.0.17:6042 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.17        state:D stack:24456 pid:6042  tgid:6042  ppid:5993   task_flags:0x400140 flags:0x00004004
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5357 [inline]
 __schedule+0x1798/0x4cc0 kernel/sched/core.c:6961
 __schedule_loop kernel/sched/core.c:7043 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:7058
 io_schedule+0x80/0xd0 kernel/sched/core.c:7903
 bit_wait_io+0x11/0xd0 kernel/sched/wait_bit.c:250
 __wait_on_bit+0xb6/0x310 kernel/sched/wait_bit.c:52
 out_of_line_wait_on_bit+0x123/0x170 kernel/sched/wait_bit.c:67
 wait_on_buffer include/linux/buffer_head.h:420 [inline]
 ext4_read_bh+0x20d/0x260 fs/ext4/super.c:207
 ext4_read_bh_lock fs/ext4/super.c:220 [inline]
 __ext4_sb_bread_gfp+0x1c9/0x210 fs/ext4/super.c:242
 ext4_sb_bread_unmovable fs/ext4/super.c:265 [inline]
 ext4_load_super fs/ext4/super.c:5063 [inline]
 __ext4_fill_super fs/ext4/super.c:5267 [inline]
 ext4_fill_super+0x802/0x6090 fs/ext4/super.c:5728
 get_tree_bdev_flags+0x40b/0x4d0 fs/super.c:1692
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1752
 do_new_mount+0x2a2/0xa30 fs/namespace.c:3810
 do_mount fs/namespace.c:4138 [inline]
 __do_sys_mount fs/namespace.c:4349 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4326
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f733498ebe9
RSP: 002b:00007ffe0adbf068 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f7334bc5fa0 RCX: 00007f733498ebe9
RDX: 0000200000000000 RSI: 0000200000000040 RDI: 0000200000000100
RBP: 00007f7334a11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000200000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7334bc5fa0 R14: 00007f7334bc5fa0 R15: 0000000000000005
 </TASK>
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x39e/0x3d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:332 [inline]
 watchdog+0xf60/0xfa0 kernel/hung_task.c:495
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x47c/0x820 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:pv_native_safe_halt+0x13/0x20 arch/x86/kernel/paravirt.c:82
Code: cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 83 0f 22 00 f3 0f 1e fa fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90 90 90 90 90
RSP: 0018:ffffc90000197de0 EFLAGS: 000002c2
RAX: a34074f8f13bed00 RBX: ffffffff8197ac78 RCX: a34074f8f13bed00
RDX: 0000000000000001 RSI: ffffffff8c04e5e0 RDI: ffffffff8197ac78
RBP: ffffc90000197f10 R08: ffff8880b8732f9b R09: 1ffff110170e65f3
R10: dffffc0000000000 R11: ffffed10170e65f4 R12: ffffffff8fe52d30
R13: 0000000000000001 R14: 0000000000000001 R15: 1ffff11003a55b40
FS:  0000000000000000(0000) GS:ffff8881258c4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056389163e5d0 CR3: 00000000754ec000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:757
 default_idle_call+0x74/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:190 [inline]
 do_idle+0x1e8/0x510 kernel/sched/idle.c:330
 cpu_startup_entry+0x44/0x60 kernel/sched/idle.c:428
 start_secondary+0x101/0x110 arch/x86/kernel/smpboot.c:315
 common_startup_64+0x13e/0x147
 </TASK>


---
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