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fb_deferred_io_work() This is in 5.15.149 tag, and this is introduced by a set of commits: 2655757a3f10 fbdev: flush deferred IO before closing 15492bab7393 fbdev: Fix incorrect page mapping clearance at fb_deferred_io_release() 87b9802ca824 fbdev: Fix invalid page access after closing deferred I/O devices 9a95fc04261f fbdev: Rename pagelist to pagereflist for deferred I/O 186b89659c4c fbdev: Track deferred-I/O pages in pageref struct e79b2b2aadef fbdev: defio: fix the pagelist corruption 0616b00a31d6 fbdev: Don't sort deferred-I/O pages by default 5d3aff76a316 fbdev/defio: Early-out if page is already enlisted I then tried if it could be reproducible on upstream kernel as well, and it did. below is the call trace with latest 6.9-rc4 based kernel. I have enabled the LOCKDEP to get locking related information. INFO: task kworker/0:3:1077 blocked for more than 122 seconds. Not tainted 6.9.0-rc4+ #54 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:kworker/0:3 state:D stack:0 pid:1077 tgid:1077 ppid:2 flags:0x00004000 Workqueue: events fb_deferred_io_work Call Trace: __schedule (kernel/sched/core.c:5409 kernel/sched/core.c:6746) ? __pfx___schedule (kernel/sched/core.c:6617) ? schedule (kernel/sched/core.c:6804 kernel/sched/core.c:6837) ? __pfx___lock_release (kernel/locking/lockdep.c:5406) ? schedule (kernel/sched/core.c:6804 kernel/sched/core.c:6837) schedule (./arch/x86/include/asm/preempt.h:84 kernel/sched/core.c:6824 kernel/sched/core.c:6838) io_schedule (kernel/sched/core.c:9019 kernel/sched/core.c:9045) folio_wait_bit_common (mm/filemap.c:1272) ? __pfx_folio_wait_bit_common (mm/filemap.c:1206) ? __pfx___mutex_lock (kernel/locking/mutex.c:751) ? lock_acquire.part.0 (kernel/locking/lockdep.c:467 kernel/locking/lockdep.c:5756) ? __pfx_wake_page_function (mm/filemap.c:1091) ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5719) fb_deferred_io_work (./include/linux/pagemap.h:1069 drivers/video/fbdev/core/fb_defio.c:248) ? lock_acquire (./include/trace/events/lock.h:24 kernel/locking/lockdep.c:5725) process_one_work (kernel/workqueue.c:3254) ? __pfx_lock_acquire.part.0 (kernel/locking/lockdep.c:5719) ? __pfx_process_one_work (kernel/workqueue.c:3156) ? assign_work (kernel/workqueue.c:1210) worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416) ? __kthread_parkme (kernel/kthread.c:293) ? __pfx_worker_thread (kernel/workqueue.c:3362) kthread (kernel/kthread.c:388) ? __pfx_kthread (kernel/kthread.c:341) ret_from_fork (arch/x86/kernel/process.c:147) ? __pfx_kthread (kernel/kthread.c:341) ret_from_fork_asm (arch/x86/entry/entry_64.S:257) INFO: task r:2664 blocked for more than 123 seconds. Not tainted 6.9.0-rc4+ #54 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. task:r state:D stack:0 pid:2664 tgid:2664 ppid:2618 flags:0x00000002 Call Trace: __schedule (kernel/sched/core.c:5409 kernel/sched/core.c:6746) ? __pfx___schedule (kernel/sched/core.c:6617) ? schedule (kernel/sched/core.c:6804 kernel/sched/core.c:6837) ? __pfx___lock_release (kernel/locking/lockdep.c:5406) ? schedule (kernel/sched/core.c:6804 kernel/sched/core.c:6837) schedule (./arch/x86/include/asm/preempt.h:84 kernel/sched/core.c:6824 kernel/sched/core.c:6838) schedule_timeout (kernel/time/timer.c:2559) ? __pfx_schedule_timeout (kernel/time/timer.c:2544) ? mark_lock.part.0 (./arch/x86/include/asm/bitops.h:227 /arch/x86/include/asm/bitops.h:239 /include/asm-generic/bitops/instrumented-non-atomic.h:142 kernel/locking/lockdep.c:228 kernel/locking/lockdep.c:4656) ? mark_held_locks (kernel/locking/lockdep.c:4274) ? lockdep_hardirqs_on_prepare.part.0 (kernel/locking/lockdep.c:4300 kernel/locking/lockdep.c:4359) __wait_for_common (kernel/sched/completion.c:95 kernel/sched/completion.c:116) ? __pfx_schedule_timeout (kernel/time/timer.c:2544) ? __pfx___wait_for_common (kernel/sched/completion.c:110) ? start_flush_work (kernel/workqueue.c:4192) __flush_work (kernel/workqueue.c:4207) ? __pfx___flush_work (kernel/workqueue.c:4195) ? __pfx_wq_barrier_func (kernel/workqueue.c:3742) ? flush_delayed_work (kernel/workqueue.c:4249) ? __pfx_fb_release (drivers/video/fbdev/core/fb_chrdev.c:375) fb_deferred_io_lastclose (drivers/video/fbdev/core/fb_defio.c:321) ? __pfx_fb_release (drivers/video/fbdev/core/fb_chrdev.c:375) fb_deferred_io_release (drivers/video/fbdev/core/fb_defio.c:333) fb_release (drivers/video/fbdev/core/fb_chrdev.c:383) ? __pfx_fb_release (drivers/video/fbdev/core/fb_chrdev.c:375) __fput (fs/file_table.c:422) task_work_run (kernel/task_work.c:180 (discriminator 1)) ? __pfx_task_work_run (kernel/task_work.c:148) ? do_raw_spin_unlock (./arch/x86/include/asm/paravirt.h:589 /arch/x86/include/asm/qspinlock.h:57 kernel/locking/spinlock_debug.c:142) do_exit (kernel/exit.c:879) ? do_raw_spin_lock (./arch/x86/include/asm/atomic.h:115 /include/linux/atomic/atomic-arch-fallback.h:2170 /include/linux/atomic/atomic-instrumented.h:1302 /include/asm-generic/qspinlock.h:111 kernel/locking/spinlock_debug.c:116) ? __pfx_do_exit (kernel/exit.c:819) ? __pfx_do_raw_spin_lock (kernel/locking/spinlock_debug.c:114) do_group_exit (kernel/exit.c:1008) __x64_sys_exit_group (kernel/exit.c:1036) do_syscall_64 (arch/x86/entry/common.c:52 arch/x86/entry/common.c:83) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:130) RIP: 0033:0x7f9cfe71e5f1 RSP: 002b:00007ffd636aec08 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 RAX: ffffffffffffffda RBX: 00007f9cfe7fc510 RCX: 00007f9cfe71e5f1 RDX: 000000000000003c RSI: 00000000000000e7 RDI: 0000000000000000 RBP: 0000000000000000 R08: ffffffffffffff80 R09: 0000000000000000 R10: 0000000000000020 R11: 0000000000000246 R12: 00007f9cfe7fc510 R13: 0000000000000000 R14: 00007f9cfe7fc9e8 R15: 00007f9cfe7fca00 Showing all locks held in the system: 1 lock held by khungtaskd/50: #0: ffffffff950219c0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks (./include/linux/rcupdate.h:329 (discriminator 1) /include/linux/rcupdate.h:781 (discriminator 1) kernel/locking/lockdep.c:6614 (discriminator 1)) 3 locks held by kworker/0:3/1077: #0: ffff88810005ad48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work (kernel/workqueue.c:3229) #1: ffff8881080dfd98 ((work_completion)(&(&info->deferred_work)->work)){+.+.}-{0:0}, at: process_one_work (kernel/workqueue.c:3230) #2: ffff88811416db38 (&fbdefio->lock){+.+.}-{3:3}, at: fb_deferred_io_work (drivers/video/fbdev/core/fb_defio.c:246) 1 lock held by r/2664: #0: ffff8881141fe078 (&fb_info->lock){+.+.}-{3:3}, at: fb_release (drivers/video/fbdev/core/fb_chrdev.c:380) Syzkaller initially generated a long reproducer, Vegard simplified it to the one below C repro: #define _GNU_SOURCE #include #include #include #include int main(void) { int fd = open("/dev/fb0", O_RDWR, 0); char *ptr = (char *) 0x20000000ul; mmap(ptr, 4096, PROT_WRITE, MAP_FIXED | MAP_SHARED, fd, 0xff000); *ptr = 0; mmap(ptr, 4096, PROT_WRITE, MAP_FIXED | MAP_SHARED, fd, 0); *ptr = 0; return 0; } This needs to be run as root to see the hang in 122 seconds. 238 static void fb_deferred_io_work(struct work_struct *work) 239 { 240 struct fb_info *info = container_of(work, struct fb_info, deferred_work.work); 241 struct fb_deferred_io_pageref *pageref, *next; 242 struct fb_deferred_io *fbdefio = info->fbdefio; 243 244 /* here we mkclean the pages, then do all deferred IO */ 245 mutex_lock(&fbdefio->lock); 246 list_for_each_entry(pageref, &fbdefio->pagereflist, list) { 247 struct page *cur = pageref->page; 248 lock_page(cur); 249 page_mkclean(cur); 250 unlock_page(cur); 251 } It is stalling on lock_page() in fb_deferred_io_work() I will be happy to try any patches and report back. Thanks, Harshit