Re: [syzbot] [dri?] possible deadlock in modeset_lock

[Daniel Vetter]

On Tue, Jul 09, 2024 at 06:54:26AM -0700, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    661e504db04c Merge tag 'for-6.10-rc6-tag' of git://git.ker..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=144e9f99980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=864caee5f78cab51
> dashboard link: https://syzkaller.appspot.com/bug?extid=6cebc1af246fe020a2f0
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/3e115f4e545a/disk-661e504d.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/48cfbafd84c8/vmlinux-661e504d.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/b19b9de9b5fd/bzImage-661e504d.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+6cebc1af246fe020a2f0@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.10.0-rc6-syzkaller-00163-g661e504db04c #0 Not tainted
> ------------------------------------------------------
> syz.3.2274/16483 is trying to acquire lock:
> ffff88807aca9e18 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0xaa/0x120 mm/memory.c:6234
> 
> but task is already holding lock:
> ffff88801fc08518 (crtc_ww_class_mutex){+.+.}-{3:3}, at: modeset_lock+0x2bf/0x650 drivers/gpu/drm/drm_modeset_lock.c:314
> 
> which lock already depends on the new lock.
> 
> 
> the existing dependency chain (in reverse order) is:
> 
> -> #8 (crtc_ww_class_mutex){+.+.}-{3:3}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        __mutex_lock_common kernel/locking/mutex.c:608 [inline]
>        __ww_mutex_lock+0x1ac/0x2790 kernel/locking/mutex.c:759
>        ww_mutex_lock+0x40/0x1f0 kernel/locking/mutex.c:876
>        modeset_lock+0x2bf/0x650 drivers/gpu/drm/drm_modeset_lock.c:314
>        drmm_mode_config_init+0xe91/0x17d0 drivers/gpu/drm/drm_mode_config.c:454
>        vkms_modeset_init drivers/gpu/drm/vkms/vkms_drv.c:156 [inline]
>        vkms_create drivers/gpu/drm/vkms/vkms_drv.c:215 [inline]
>        vkms_init+0x380/0x730 drivers/gpu/drm/vkms/vkms_drv.c:252
>        do_one_initcall+0x24a/0x880 init/main.c:1267
>        do_initcall_level+0x157/0x210 init/main.c:1329
>        do_initcalls+0x3f/0x80 init/main.c:1345
>        kernel_init_freeable+0x435/0x5d0 init/main.c:1578
>        kernel_init+0x1d/0x2b0 init/main.c:1467
>        ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> -> #7 (crtc_ww_class_acquire){+.+.}-{0:0}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        ww_acquire_init include/linux/ww_mutex.h:149 [inline]
>        drm_modeset_acquire_init+0x1b7/0x360 drivers/gpu/drm/drm_modeset_lock.c:250
>        drm_client_modeset_commit_atomic+0xd5/0x7e0 drivers/gpu/drm/drm_client_modeset.c:1002
>        drm_client_modeset_commit_locked+0xe0/0x520 drivers/gpu/drm/drm_client_modeset.c:1166
>        drm_client_modeset_commit+0x4a/0x70 drivers/gpu/drm/drm_client_modeset.c:1192
>        __drm_fb_helper_restore_fbdev_mode_unlocked+0xc3/0x170 drivers/gpu/drm/drm_fb_helper.c:251
>        drm_fb_helper_set_par+0xaf/0x100 drivers/gpu/drm/drm_fb_helper.c:1347
>        fbcon_init+0x112d/0x2100 drivers/video/fbdev/core/fbcon.c:1093
>        visual_init+0x2e9/0x660 drivers/tty/vt/vt.c:1011
>        do_bind_con_driver+0x863/0xf60 drivers/tty/vt/vt.c:3833
>        do_take_over_console+0x5e7/0x750 drivers/tty/vt/vt.c:4399
>        do_fbcon_takeover+0x11a/0x200 drivers/video/fbdev/core/fbcon.c:531
>        do_fb_registered drivers/video/fbdev/core/fbcon.c:2968 [inline]
>        fbcon_fb_registered+0x364/0x620 drivers/video/fbdev/core/fbcon.c:2988
>        do_register_framebuffer drivers/video/fbdev/core/fbmem.c:449 [inline]
>        register_framebuffer+0x66f/0x820 drivers/video/fbdev/core/fbmem.c:515
>        __drm_fb_helper_initial_config_and_unlock+0x1716/0x1df0 drivers/gpu/drm/drm_fb_helper.c:1871
>        drm_fbdev_generic_client_hotplug+0x16e/0x230 drivers/gpu/drm/drm_fbdev_generic.c:278
>        drm_client_register+0x181/0x210 drivers/gpu/drm/drm_client.c:141
>        vkms_create drivers/gpu/drm/vkms/vkms_drv.c:226 [inline]
>        vkms_init+0x5f5/0x730 drivers/gpu/drm/vkms/vkms_drv.c:252
>        do_one_initcall+0x24a/0x880 init/main.c:1267
>        do_initcall_level+0x157/0x210 init/main.c:1329
>        do_initcalls+0x3f/0x80 init/main.c:1345
>        kernel_init_freeable+0x435/0x5d0 init/main.c:1578
>        kernel_init+0x1d/0x2b0 init/main.c:1467
>        ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> -> #6 (&client->modeset_mutex){+.+.}-{3:3}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        __mutex_lock_common kernel/locking/mutex.c:608 [inline]
>        __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
>        drm_client_modeset_probe+0x3b9/0x5480 drivers/gpu/drm/drm_client_modeset.c:832
>        __drm_fb_helper_initial_config_and_unlock+0x112/0x1df0 drivers/gpu/drm/drm_fb_helper.c:1848
>        drm_fbdev_generic_client_hotplug+0x16e/0x230 drivers/gpu/drm/drm_fbdev_generic.c:278
>        drm_client_register+0x181/0x210 drivers/gpu/drm/drm_client.c:141
>        vkms_create drivers/gpu/drm/vkms/vkms_drv.c:226 [inline]
>        vkms_init+0x5f5/0x730 drivers/gpu/drm/vkms/vkms_drv.c:252
>        do_one_initcall+0x24a/0x880 init/main.c:1267
>        do_initcall_level+0x157/0x210 init/main.c:1329
>        do_initcalls+0x3f/0x80 init/main.c:1345
>        kernel_init_freeable+0x435/0x5d0 init/main.c:1578
>        kernel_init+0x1d/0x2b0 init/main.c:1467
>        ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> -> #5 (&helper->lock){+.+.}-{3:3}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        __mutex_lock_common kernel/locking/mutex.c:608 [inline]
>        __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
>        __drm_fb_helper_restore_fbdev_mode_unlocked+0xa2/0x170 drivers/gpu/drm/drm_fb_helper.c:242
>        drm_fb_helper_set_par+0xaf/0x100 drivers/gpu/drm/drm_fb_helper.c:1347
>        fbcon_init+0x112d/0x2100 drivers/video/fbdev/core/fbcon.c:1093
>        visual_init+0x2e9/0x660 drivers/tty/vt/vt.c:1011
>        do_bind_con_driver+0x863/0xf60 drivers/tty/vt/vt.c:3833
>        do_take_over_console+0x5e7/0x750 drivers/tty/vt/vt.c:4399
>        do_fbcon_takeover+0x11a/0x200 drivers/video/fbdev/core/fbcon.c:531
>        do_fb_registered drivers/video/fbdev/core/fbcon.c:2968 [inline]
>        fbcon_fb_registered+0x364/0x620 drivers/video/fbdev/core/fbcon.c:2988
>        do_register_framebuffer drivers/video/fbdev/core/fbmem.c:449 [inline]
>        register_framebuffer+0x66f/0x820 drivers/video/fbdev/core/fbmem.c:515
>        __drm_fb_helper_initial_config_and_unlock+0x1716/0x1df0 drivers/gpu/drm/drm_fb_helper.c:1871
>        drm_fbdev_generic_client_hotplug+0x16e/0x230 drivers/gpu/drm/drm_fbdev_generic.c:278
>        drm_client_register+0x181/0x210 drivers/gpu/drm/drm_client.c:141
>        vkms_create drivers/gpu/drm/vkms/vkms_drv.c:226 [inline]
>        vkms_init+0x5f5/0x730 drivers/gpu/drm/vkms/vkms_drv.c:252
>        do_one_initcall+0x24a/0x880 init/main.c:1267
>        do_initcall_level+0x157/0x210 init/main.c:1329
>        do_initcalls+0x3f/0x80 init/main.c:1345
>        kernel_init_freeable+0x435/0x5d0 init/main.c:1578
>        kernel_init+0x1d/0x2b0 init/main.c:1467
>        ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:147
>        ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> 
> -> #4 (console_lock){+.+.}-{0:0}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        console_lock+0x164/0x1b0 kernel/printk/printk.c:2665
>        bch2_print_string_as_lines+0x20/0xc0 fs/bcachefs/util.c:264

This function is very wrong, you're not allowed to call console_lock when
holding pretty much any other lock. I'll type up a patch to put a trylock
in there.

Definitely not a drm issue, we nest potential might_fault within
crtc_ww_class absolutely everywhere.
-Sima

>        bch2_fsck_err+0xd44/0x1450 fs/bcachefs/error.c:352
>        bch2_gc_mark_key+0xa69/0x1010 fs/bcachefs/btree_gc.c:586
>        bch2_gc_btree fs/bcachefs/btree_gc.c:664 [inline]
>        bch2_gc_btrees fs/bcachefs/btree_gc.c:697 [inline]
>        bch2_check_allocations+0x3668/0xccc0 fs/bcachefs/btree_gc.c:1224
>        bch2_run_recovery_pass+0xf2/0x1e0 fs/bcachefs/recovery_passes.c:182
>        bch2_run_recovery_passes+0x19e/0x820 fs/bcachefs/recovery_passes.c:225
>        bch2_fs_recovery+0x2386/0x3730 fs/bcachefs/recovery.c:813
>        bch2_fs_start+0x356/0x5b0 fs/bcachefs/super.c:1035
>        bch2_fs_open+0xa8d/0xdf0 fs/bcachefs/super.c:2132
>        bch2_mount+0x6b0/0x13a0 fs/bcachefs/fs.c:1926
>        legacy_get_tree+0xf0/0x190 fs/fs_context.c:662
>        vfs_get_tree+0x92/0x2a0 fs/super.c:1789
>        do_new_mount+0x2be/0xb40 fs/namespace.c:3352
>        do_mount fs/namespace.c:3692 [inline]
>        __do_sys_mount fs/namespace.c:3898 [inline]
>        __se_sys_mount+0x2d9/0x3c0 fs/namespace.c:3875
>        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>        do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> -> #3 (&c->fsck_error_msgs_lock){+.+.}-{3:3}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        __mutex_lock_common kernel/locking/mutex.c:608 [inline]
>        __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
>        bch2_fsck_err+0x311/0x1450 fs/bcachefs/error.c:239
>        bch2_gc_done fs/bcachefs/btree_gc.c:767 [inline]
>        bch2_check_allocations+0x7d39/0xccc0 fs/bcachefs/btree_gc.c:1233
>        bch2_run_recovery_pass+0xf2/0x1e0 fs/bcachefs/recovery_passes.c:182
>        bch2_run_recovery_passes+0x19e/0x820 fs/bcachefs/recovery_passes.c:225
>        bch2_fs_recovery+0x2386/0x3730 fs/bcachefs/recovery.c:813
>        bch2_fs_start+0x356/0x5b0 fs/bcachefs/super.c:1035
>        bch2_fs_open+0xa8d/0xdf0 fs/bcachefs/super.c:2132
>        bch2_mount+0x6b0/0x13a0 fs/bcachefs/fs.c:1926
>        legacy_get_tree+0xf0/0x190 fs/fs_context.c:662
>        vfs_get_tree+0x92/0x2a0 fs/super.c:1789
>        do_new_mount+0x2be/0xb40 fs/namespace.c:3352
>        do_mount fs/namespace.c:3692 [inline]
>        __do_sys_mount fs/namespace.c:3898 [inline]
>        __se_sys_mount+0x2d9/0x3c0 fs/namespace.c:3875
>        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>        do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> -> #2 (&c->mark_lock){++++}-{0:0}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        percpu_down_read+0x44/0x1b0 include/linux/percpu-rwsem.h:51
>        __bch2_disk_reservation_add+0x97/0x620 fs/bcachefs/buckets.c:1530
>        bch2_disk_reservation_add fs/bcachefs/buckets.h:430 [inline]
>        bch2_folio_reservation_get+0x2d1/0x600 fs/bcachefs/fs-io-pagecache.c:446
>        bch2_page_mkwrite+0x8a5/0xd90 fs/bcachefs/fs-io-pagecache.c:616
>        do_page_mkwrite+0x19d/0x480 mm/memory.c:3093
>        do_shared_fault mm/memory.c:4993 [inline]
>        do_fault mm/memory.c:5055 [inline]
>        do_pte_missing mm/memory.c:3897 [inline]
>        handle_pte_fault+0x1290/0x7090 mm/memory.c:5381
>        __handle_mm_fault mm/memory.c:5524 [inline]
>        handle_mm_fault+0x10df/0x1ba0 mm/memory.c:5689
>        do_user_addr_fault arch/x86/mm/fault.c:1389 [inline]
>        handle_page_fault arch/x86/mm/fault.c:1481 [inline]
>        exc_page_fault+0x2b9/0x8c0 arch/x86/mm/fault.c:1539
>        asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
> 
> -> #1 (sb_pagefaults#2){.+.+}-{0:0}:
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
>        __sb_start_write include/linux/fs.h:1655 [inline]
>        sb_start_pagefault include/linux/fs.h:1820 [inline]
>        bch2_page_mkwrite+0x2fc/0xd90 fs/bcachefs/fs-io-pagecache.c:593
>        do_page_mkwrite+0x19d/0x480 mm/memory.c:3093
>        do_shared_fault mm/memory.c:4993 [inline]
>        do_fault mm/memory.c:5055 [inline]
>        do_pte_missing mm/memory.c:3897 [inline]
>        handle_pte_fault+0x1290/0x7090 mm/memory.c:5381
>        __handle_mm_fault mm/memory.c:5524 [inline]
>        handle_mm_fault+0x10df/0x1ba0 mm/memory.c:5689
>        do_user_addr_fault arch/x86/mm/fault.c:1389 [inline]
>        handle_page_fault arch/x86/mm/fault.c:1481 [inline]
>        exc_page_fault+0x2b9/0x8c0 arch/x86/mm/fault.c:1539
>        asm_exc_page_fault+0x26/0x30 arch/x86/include/asm/idtentry.h:623
> 
> -> #0 (&mm->mmap_lock){++++}-{3:3}:
>        check_prev_add kernel/locking/lockdep.c:3134 [inline]
>        check_prevs_add kernel/locking/lockdep.c:3253 [inline]
>        validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3869
>        __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
>        lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>        __might_fault+0xc6/0x120 mm/memory.c:6234
>        drm_mode_object_get_properties+0x222/0x4d0 drivers/gpu/drm/drm_mode_object.c:406
>        drm_mode_obj_get_properties_ioctl+0x350/0x610 drivers/gpu/drm/drm_mode_object.c:458
>        drm_ioctl_kernel+0x33c/0x440 drivers/gpu/drm/drm_ioctl.c:744
>        drm_ioctl+0x611/0xad0 drivers/gpu/drm/drm_ioctl.c:841
>        vfs_ioctl fs/ioctl.c:51 [inline]
>        __do_sys_ioctl fs/ioctl.c:907 [inline]
>        __se_sys_ioctl+0xfe/0x170 fs/ioctl.c:893
>        do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>        do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>        entry_SYSCALL_64_after_hwframe+0x77/0x7f
> 
> other info that might help us debug this:
> 
> Chain exists of:
>   &mm->mmap_lock --> crtc_ww_class_acquire --> crtc_ww_class_mutex
> 
>  Possible unsafe locking scenario:
> 
>        CPU0                    CPU1
>        ----                    ----
>   lock(crtc_ww_class_mutex);
>                                lock(crtc_ww_class_acquire);
>                                lock(crtc_ww_class_mutex);
>   rlock(&mm->mmap_lock);
> 
>  *** DEADLOCK ***
> 
> 2 locks held by syz.3.2274/16483:
>  #0: ffffc900044d7b30 (crtc_ww_class_acquire){+.+.}-{0:0}, at: drm_mode_obj_get_properties_ioctl+0x1d3/0x610 drivers/gpu/drm/drm_mode_object.c:446
>  #1: ffff88801fc08518 (crtc_ww_class_mutex){+.+.}-{3:3}, at: modeset_lock+0x2bf/0x650 drivers/gpu/drm/drm_modeset_lock.c:314
> 
> stack backtrace:
> CPU: 1 PID: 16483 Comm: syz.3.2274 Not tainted 6.10.0-rc6-syzkaller-00163-g661e504db04c #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:88 [inline]
>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
>  check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2187
>  check_prev_add kernel/locking/lockdep.c:3134 [inline]
>  check_prevs_add kernel/locking/lockdep.c:3253 [inline]
>  validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3869
>  __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
>  lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
>  __might_fault+0xc6/0x120 mm/memory.c:6234
>  drm_mode_object_get_properties+0x222/0x4d0 drivers/gpu/drm/drm_mode_object.c:406
>  drm_mode_obj_get_properties_ioctl+0x350/0x610 drivers/gpu/drm/drm_mode_object.c:458
>  drm_ioctl_kernel+0x33c/0x440 drivers/gpu/drm/drm_ioctl.c:744
>  drm_ioctl+0x611/0xad0 drivers/gpu/drm/drm_ioctl.c:841
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:907 [inline]
>  __se_sys_ioctl+0xfe/0x170 fs/ioctl.c:893
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f7140375bd9
> Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f7141231048 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 00007f7140503f60 RCX: 00007f7140375bd9
> RDX: 00000000200002c0 RSI: 00000000c02064b9 RDI: 0000000000000003
> RBP: 00007f71403e4aa1 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 000000000000000b R14: 00007f7140503f60 R15: 00007ffdba322618
>  </TASK>
> 
> 
> ---
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch