Re: [syzbot] [fs?] [mm?] kernel BUG in __filemap_add_folio

[syzbot <syzbot+4d3cc33ef7a77041efa6@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: task hung in set_blocksize

INFO: task syz.0.1117:9015 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.1117      state:D stack:27296 pid:9015  tgid:9012  ppid:6400   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7017
 rwsem_down_write_slowpath+0x521/0x1310 kernel/locking/rwsem.c:1185
 __down_write_common kernel/locking/rwsem.c:1317 [inline]
 __down_write kernel/locking/rwsem.c:1326 [inline]
 down_write+0x1d6/0x200 kernel/locking/rwsem.c:1591
 filemap_invalidate_lock include/linux/fs.h:1082 [inline]
 set_blocksize+0x20f/0x500 block/bdev.c:204
 blkdev_bszset+0x19b/0x240 block/ioctl.c:634
 blkdev_ioctl+0x2ef/0x6e0 block/ioctl.c:773
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f939698eba9
RSP: 002b:00007f93978b0038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9396bd5fa0 RCX: 00007f939698eba9
RDX: 0000200000000980 RSI: 0000000040081271 RDI: 0000000000000005
RBP: 00007f9396a11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9396bd6038 R14: 00007f9396bd5fa0 R15: 00007ffd57bc7cc8
 </TASK>
INFO: task syz.1.1118:9013 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.1.1118      state:D stack:27536 pid:9013  tgid:9013  ppid:6399   task_flags:0x440040 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x1139/0x6150 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0xe7/0x3a0 kernel/sched/core.c:6960
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7017
 rwsem_down_read_slowpath+0x64b/0xbf0 kernel/locking/rwsem.c:1086
 __down_read_common kernel/locking/rwsem.c:1261 [inline]
 __down_read kernel/locking/rwsem.c:1274 [inline]
 down_read+0xef/0x460 kernel/locking/rwsem.c:1539
 filemap_invalidate_lock_shared include/linux/fs.h:1092 [inline]
 page_cache_ra_unbounded+0x20c/0x9e0 mm/readahead.c:233
 do_page_cache_ra mm/readahead.c:332 [inline]
 page_cache_ra_order+0x9c8/0xd80 mm/readahead.c:536
 do_sync_mmap_readahead mm/filemap.c:3400 [inline]
 filemap_fault+0x16ac/0x29d0 mm/filemap.c:3549
 __do_fault+0x10d/0x490 mm/memory.c:5320
 do_shared_fault mm/memory.c:5819 [inline]
 do_fault+0x302/0x1ad0 mm/memory.c:5893
 do_pte_missing mm/memory.c:4401 [inline]
 handle_pte_fault mm/memory.c:6273 [inline]
 __handle_mm_fault+0x1919/0x2bb0 mm/memory.c:6411
 handle_mm_fault+0x3fe/0xad0 mm/memory.c:6580
 do_user_addr_fault+0x60c/0x1370 arch/x86/mm/fault.c:1336
 handle_page_fault arch/x86/mm/fault.c:1476 [inline]
 exc_page_fault+0x64/0xc0 arch/x86/mm/fault.c:1532
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7f55be158088
RSP: 002b:00007ffe04457bf8 EFLAGS: 00010202
RAX: 0000200000000080 RBX: 0000000000000004 RCX: 0030626c6c756e2f
RDX: 000000000000000c RSI: 6c756e2f7665642f RDI: 0000200000000080
RBP: 00007f55be3d7da0 R08: 0000001b33920000 R09: 0000000000000001
R10: 0000000000000001 R11: 0000000000000009 R12: 00007f55be3d5fac
R13: 00007f55be3d5fa0 R14: fffffffffffffffe R15: 00007ffe04457d10
 </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 10/25/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x27b/0x390 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x29c/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:160 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x133/0x180 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xe66/0x1180 kernel/hung_task.c:515
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </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 10/25/2025
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:82
Code: 86 6c 02 c3 cc cc cc cc 0f 1f 00 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 13 69 1f 00 fb f4 <e9> cc 35 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffc90000197de8 EFLAGS: 000002c6
RAX: 000000000003249c RBX: 0000000000000001 RCX: ffffffff8b6af6d9
RDX: ffffed10170a673e RSI: ffffffff8bf29c80 RDI: ffffffff819335dd
RBP: ffffed1003b56498 R08: 0000000000000000 R09: ffffed10170a673d
R10: ffff8880b85339eb R11: 0000000000005e25 R12: 0000000000000001
R13: ffff88801dab24c0 R14: ffffffff908653d0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888124a4e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055555cc735c8 CR3: 000000005dfbe000 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:767
 default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:191 [inline]
 do_idle+0x38d/0x510 kernel/sched/idle.c:332
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:430
 start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x148
 </TASK>


Tested on:

commit:         0048fbb4 Merge tag 'locking-futex-2025-12-10' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12b6deb4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=219582171d92591c
dashboard link: https://syzkaller.appspot.com/bug?extid=4d3cc33ef7a77041efa6
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=163fda1a580000