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INFO: task hung in writeback_iter (3)

Status: upstream: reported C repro on 2025/08/28 09:40
Subsystems: mm fs
[Documentation on labels]
Reported-by: syzbot+1e3ff4b07c16ca0f6fe2@syzkaller.appspotmail.com
First crash: 269d, last: 38d
Cause bisection: failed (error log, bisect log)
  
Fix bisection: failed (error log, bisect log)
  
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
714691f4-012f-44cc-86a7-b932b7d393d5 assessment-security 💥 INFO: task hung in writeback_iter (3) 2026/05/15 10:26 2026/05/15 10:26 2026/05/15 10:27 9cd3beaadf14b3a22d15fd97a0bf081ee41ebe01 failed to run ["make" "KERNELVERSION=syzkaller" "KERNELRELEASE=syzkaller" "LOCALVERSION=-syzkaller" "-j" "32" "ARCH=x86_64" "CC=ccache clang" "LD=ld.lld" "O=/app/workdir/cache/build/ff9339b10c757482738e9843d58df367f54935c0" "-s" "bzImage" "compile_commands.json"]: exit status 2 Root cause: error: unable to open output file 'drivers/gpio/gpiolib.o': 'No such file or directory' fatal error: error in backend: IO failure on output stream: No space left on device PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace, preprocessed source, and associated run script. Stack dump: 0. Program arguments: /usr/bin/clang -Wp,-MMD,arch/x86/lib/.copy_user_uncached_64.o.d -nostdinc -I/app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/arch/x86/include -I./arch/x86/include/generated -I/app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/include -I./include -I/app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/arch/x86/include/uapi -I./arch/x86/include/generated/uapi -I/app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/include/uapi -I./include/generated/uapi -include /app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/include/linux/compiler-version.h -include /app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/include/linux/kconfig.h -include /app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/include/linux/compiler_types.h -D__KERNEL__ --target=x86_64-linux-gnu -fintegrated-as -Werror=unknown-warning-option -Werror=ignored-optimization-argument -Werror=option-ignored -Werror=unused-command-line-argument -fmacro-prefix-map=/app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/= -std=gnu11 -fshort-wchar -funsigned-char -fno-common -fno-PIE -fno-strict-aliasing -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -mno-sse4a -fcf-protection=branch -fno-jump-tables -m64 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -mstack-alignment=8 -mskip-rax-setup -march=x86-64 -mtune=generic -mno-red-zone -mcmodel=kernel -mstack-protector-guard-reg=gs -mstack-protector-guard-symbol=__ref_stack_chk_guard -Wno-sign-compare -fno-asynchronous-unwind-tables -mretpoline-external-thunk -mindirect-branch-cs-prefix -mfunction-return=thunk-extern -fpatchable-function-entry=16,16 -fno-delete-null-pointer-checks -O2 -fstack-protector-strong -fomit-frame-pointer -ftrivial-auto-var-init=zero -fno-stack-clash-protection -falign-functions=16 -fstrict-flex-arrays=3 -fms-extensions -fno-strict-overflow -fno-stack-check -fno-builtin-wcslen -Wall -Wextra -Wundef -Werror=implicit-function-declaration -Werror=implicit-int -Werror=return-type -Werror=strict-prototypes -Wno-format-security -Wno-trigraphs -Wno-frame-address -Wno-address-of-packed-member -Wmissing-declarations -Wmissing-prototypes -Wframe-larger-than=2048 -Wno-gnu -Wno-microsoft-anon-tag -Wno-format-overflow-non-kprintf -Wno-format-truncation-non-kprintf -Wno-default-const-init-unsafe -Wno-type-limits -Wno-pointer-sign -Wcast-function-type -Wno-unterminated-string-initialization -Wimplicit-fallthrough -Werror=date-time -Werror=incompatible-pointer-types -Wenum-conversion -Wunused -Wno-unused-but-set-variable -Wno-unused-const-variable -Wno-format-overflow -Wno-override-init -Wno-pointer-to-enum-cast -Wno-tautological-constant-out-of-range-compare -Wno-unaligned-access -Wno-enum-compare-conditional -Wno-missing-field-initializers -Wno-shift-negative-value -Wno-enum-enum-conversion -Wno-sign-compare -Wno-unused-parameter -g -gdwarf-4 -fsanitize=kernel-address -mllvm -asan-mapping-offset=0xdffffc0000000000 -mllvm -asan-instrumentation-with-call-threshold=10000 -mllvm -asan-stack=1 -mllvm -asan-globals=1 -mllvm -asan-kernel-mem-intrinsic-prefix=1 -fsanitize=array-bounds -fsanitize=shift -fsanitize-coverage=trace-pc -fsanitize-coverage=trace-cmp -fdebug-info-for-profiling -mllvm -enable-fs-discriminator=true -mllvm -improved-fs-discriminator=true -fbasic-block-address-map -I/app/workdir/cache/src/042850677d0d7a5f2b9b1c3afcf5d61117655d61/arch/x86/lib -Iarch/x86/lib -DKBUILD_MODFI
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[RFC PATCH] fs/hfs: fix ABBA deadlock in hfs_mdb_commit 11 (11) 2026/01/21 02:44
[syzbot] [gfs2?] INFO: task hung in writeback_iter (3) 0 (1) 2025/08/28 09:40
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in writeback_iter (2) fs mm 1 3 372d 386d 0/29 auto-obsoleted due to no activity on 2025/08/11 03:24
upstream INFO: task hung in writeback_iter mm fs 1 145 488d 597d 0/29 auto-obsoleted due to no activity on 2025/03/08 08:54
▶ ▼ Last patch testing requests (10)
Created Duration User Patch Repo Result
2026/05/09 20:38 23m retest repro upstream report log
2026/05/01 19:39 47m retest repro linux-next report log
2026/05/01 19:39 1h25m retest repro linux-next report log
2026/05/01 19:39 1h26m retest repro linux-next report log
2026/05/01 19:39 36m retest repro linux-next report log
2026/05/01 19:39 30m retest repro linux-next report log
2026/04/26 09:26 38m retest repro linux-next report log
2026/04/26 09:26 28m retest repro linux-next report log
2026/04/26 09:26 30m retest repro linux-next report log
2026/04/26 09:26 35m retest repro linux-next report log

Sample crash report:
INFO: task syz.0.17:6049 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:24280 pid:6049  tgid:6049  ppid:5965   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5298 [inline]
 __schedule+0x15dd/0x52d0 kernel/sched/core.c:6911
 __schedule_loop kernel/sched/core.c:6993 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7008
 io_schedule+0x7f/0xd0 kernel/sched/core.c:7835
 folio_wait_bit_common+0x6d8/0xbc0 mm/filemap.c:1323
 folio_lock include/linux/pagemap.h:1170 [inline]
 writeback_get_folio mm/page-writeback.c:2418 [inline]
 writeback_iter+0x8d8/0x12c0 mm/page-writeback.c:2512
 iomap_writepages+0x152/0x2e0 fs/iomap/buffered-io.c:1957
 gfs2_writepages+0x197/0x280 fs/gfs2/aops.c:174
 do_writepages+0x32e/0x550 mm/page-writeback.c:2554
 filemap_writeback mm/filemap.c:387 [inline]
 filemap_fdatawrite_range mm/filemap.c:412 [inline]
 filemap_fdatawrite+0x1e9/0x2f0 mm/filemap.c:418
 gfs2_ordered_write fs/gfs2/log.c:729 [inline]
 gfs2_log_flush+0x881/0x2510 fs/gfs2/log.c:1093
 gfs2_trans_end+0x37b/0x570 fs/gfs2/trans.c:163
 gfs2_page_mkwrite+0x14de/0x1990 fs/gfs2/file.c:535
 do_page_mkwrite+0x14d/0x310 mm/memory.c:3589
 wp_page_shared mm/memory.c:3990 [inline]
 do_wp_page+0x1a4b/0x5a00 mm/memory.c:4209
 handle_pte_fault mm/memory.c:6333 [inline]
 __handle_mm_fault mm/memory.c:6455 [inline]
 handle_mm_fault+0x1520/0x3310 mm/memory.c:6624
 do_user_addr_fault+0xa73/0x1340 arch/x86/mm/fault.c:1334
 handle_page_fault arch/x86/mm/fault.c:1474 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7fcf6cf6ae9b
RSP: 002b:00007ffd45e637b8 EFLAGS: 00010202
RAX: 0000200000000040 RBX: 0000000000000004 RCX: 0000000000736f64
RDX: 0000000000000006 RSI: 000000006f64736d RDI: 0000200000000040
RBP: fffffffffffffffe R08: 0000001b30c20000 R09: 0000000000000001
R10: 7ffffffffffffff9 R11: 0000000000000009 R12: 0000000000000000
R13: 00007fcf6d215fac R14: 000000000002bb23 R15: 00007fcf6d215fa0
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/32:
 #0: ffffffff8e75e520 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
 #0: ffffffff8e75e520 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:850 [inline]
 #0: ffffffff8e75e520 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6775
4 locks held by kworker/u8:9/3473:
 #0: ffff88801baf2148 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3251 [inline]
 #0: ffff88801baf2148 ((wq_completion)writeback){+.+.}-{0:0}, at: process_scheduled_works+0xa52/0x18c0 kernel/workqueue.c:3359
 #1: ffffc9000e23fc40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3252 [inline]
 #1: ffffc9000e23fc40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_scheduled_works+0xa8d/0x18c0 kernel/workqueue.c:3359
 #2: ffff888035e180e0 (&type->s_umount_key#54){.+.+}-{4:4}, at: super_trylock_shared+0x20/0xf0 fs/super.c:565
 #3: ffff88807de7cea0 (&sdp->sd_log_flush_lock){++++}-{4:4}, at: gfs2_log_flush+0xef/0x2510 fs/gfs2/log.c:1036
2 locks held by getty/5580:
 #0: ffff888031c210a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc9000331e2f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45c/0x13c0 drivers/tty/n_tty.c:2211
4 locks held by syz.0.17/6049:
 #0: ffff888032e421c8 (vm_lock){++++}-{0:0}, at: lock_vma_under_rcu+0x1d1/0x500 mm/mmap_lock.c:310
 #1: ffff888035e18518 (sb_pagefaults#2){.+.+}-{0:0}, at: do_page_mkwrite+0x14d/0x310 mm/memory.c:3589
 #2: ffff888035e18610 (sb_internal#2){.+.+}-{0:0}, at: gfs2_trans_begin+0x6f/0xe0 fs/gfs2/trans.c:123
 #3: ffff88807de7cea0 (&sdp->sd_log_flush_lock){++++}-{4:4}, at: gfs2_log_flush+0xef/0x2510 fs/gfs2/log.c:1036
1 lock held by gfs2_logd/syz:s/6067:
 #0: ffff88807de7cea0 (&sdp->sd_log_flush_lock){++++}-{4:4}, at: gfs2_log_flush+0xef/0x2510 fs/gfs2/log.c:1036
2 locks held by gfs2_quotad/syz/6068:
 #0: 
ffff888035e18610 (sb_internal#2){.+.+}-{0:0}, at: gfs2_trans_begin+0x6f/0xe0 fs/gfs2/trans.c:123
 #1: ffff88807de7cea0 (&sdp->sd_log_flush_lock){++++}-{4:4}, at: __gfs2_trans_begin+0x51e/0x910 fs/gfs2/trans.c:87
2 locks held by syz.1.178/6592:

=============================================

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 32 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x17a/0x300 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:161 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:346 [inline]
 watchdog+0xfd9/0x1030 kernel/hung_task.c:515
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6592 Comm: syz.1.178 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:__lock_release kernel/locking/lockdep.c:5514 [inline]
RIP: 0010:lock_release+0xa8/0x3d0 kernel/locking/lockdep.c:5889
Code: 00 0f 85 f7 01 00 00 49 81 3e 20 d4 df 93 0f 84 ea 01 00 00 9c 5b fa 48 c7 c7 b3 04 f1 8d e8 9f a2 0c 0a 65 ff 05 88 8a 7a 11 <c7> 44 24 24 01 00 00 00 83 3d 89 12 70 0e 00 0f 84 90 01 00 00 41
RSP: 0000:ffffc90005257a90 EFLAGS: 00000002
RAX: 0000000000000000 RBX: 0000000000000202 RCX: 0000000000000046
RDX: 0000000000000000 RSI: ffffffff8df104b3 RDI: ffffffff8c27be80
RBP: 0000000000000000 R08: ffffffff9a45ea47 R09: 1ffffffff348bd48
R10: dffffc0000000000 R11: fffffbfff348bd49 R12: dffffc0000000000
R13: ffffffff8496b89d R14: ffffffff8e75e520 R15: ffff88802d705b80
FS:  000055556f10b500(0000) GS:ffff888125460000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa8e498b000 CR3: 000000003403e000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 rcu_lock_release include/linux/rcupdate.h:322 [inline]
 rcu_read_unlock include/linux/rcupdate.h:881 [inline]
 blk_cgroup_congested+0x1ef/0x210 block/blk-cgroup.c:2245
 __folio_throttle_swaprate+0x3c/0x140 mm/swapfile.c:3924
 folio_throttle_swaprate include/linux/swap.h:587 [inline]
 folio_prealloc mm/memory.c:1215 [inline]
 alloc_anon_folio mm/memory.c:5209 [inline]
 do_anonymous_page mm/memory.c:5266 [inline]
 do_pte_missing+0x173e/0x3490 mm/memory.c:4475
 handle_pte_fault mm/memory.c:6317 [inline]
 __handle_mm_fault mm/memory.c:6455 [inline]
 handle_mm_fault+0x1bec/0x3310 mm/memory.c:6624
 do_user_addr_fault+0xa73/0x1340 arch/x86/mm/fault.c:1334
 handle_page_fault arch/x86/mm/fault.c:1474 [inline]
 exc_page_fault+0x6a/0xc0 arch/x86/mm/fault.c:1527
 asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:618
RIP: 0033:0x7fa8ed253b18
Code: 85 ed 74 3b 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 48 39 f0 72 1b 4d 8b 07 49 89 c1 49 29 f1 47 0f b6 0c 08 45 84 c9 74 08 <45> 88 0c 00 49 8b 47 10 48 83 c0 01 49 89 47 10 83 e9 01 73 d3 41
RSP: 002b:00007ffe9125ac20 EFLAGS: 00010202
RAX: 000000000058b000 RBX: 00007ffe9125ace0 RCX: 000000000000001e
RDX: 00000000000005ff RSI: 0000000000000400 RDI: 00007ffe9125ad80
RBP: 000000000000001f R08: 00007fa8e4400000 R09: 0000000000000001
R10: 0000200000038002 R11: 0000000000037f12 R12: 0000000000000301
R13: 00007fa8ed452620 R14: 0000000000000013 R15: 00007ffe9125ad80
 </TASK>

Crashes (18):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/17 08:32 upstream 2d1373e4246d 0737c18f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (clean fs)] ci-upstream-kasan-gce-root INFO: task hung in writeback_iter
2026/01/14 01:33 upstream b54345928fa1 d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-upstream-fs INFO: task hung in writeback_iter
2025/12/20 17:03 linux-next cc3aa43b44bd d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/26 08:40 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/26 04:18 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/25 11:55 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/25 07:29 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/25 03:09 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/24 22:18 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/24 18:22 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/24 13:53 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/24 09:34 linux-next 7fa4d8dc380f bf27483f .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2026/04/12 06:13 upstream e753c16cb3dd 38c8e246 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in writeback_iter
2026/03/31 14:21 upstream d0c3bcd5b897 aeea1c72 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in writeback_iter
2026/03/07 08:42 upstream 651690480a96 5cb44a80 .config console log report info [disk image] [vmlinux] [kernel image] ci2-upstream-fs INFO: task hung in writeback_iter
2025/09/17 18:20 upstream 5aca7966d2a7 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root INFO: task hung in writeback_iter
2025/09/07 09:23 linux-next be5d4872e528 d291dd2d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
2025/08/24 05:30 linux-next 7fa4d8dc380f bf27483f .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root INFO: task hung in writeback_iter
* Struck through repros no longer work on HEAD.