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Date:   Tue, 15 Dec 2020 17:14:11 -0800
From:   syzbot <syzbot+972b924c988834e868b2@...kaller.appspotmail.com>
To:     b.zolnierkie@...sung.com, daniel.vetter@...ll.ch,
        dri-devel@...ts.freedesktop.org, geert@...ux-m68k.org,
        gustavoars@...nel.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, natechancellor@...il.com,
        peda@...ntia.se, penguin-kernel@...ove.sakura.ne.jp,
        syzkaller-bugs@...glegroups.com
Subject: WARNING: suspicious RCU usage in modeset_lock

Hello,

syzbot found the following issue on:

HEAD commit:    94801e5c Merge tag 'pinctrl-v5.10-3' of git://git.kernel.o..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=130558c5500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=ee8a1012a5314210
dashboard link: https://syzkaller.appspot.com/bug?extid=972b924c988834e868b2
compiler:       gcc (GCC) 10.1.0-syz 20200507
userspace arch: i386

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+972b924c988834e868b2@...kaller.appspotmail.com

=============================
WARNING: suspicious RCU usage
5.10.0-rc7-syzkaller #0 Not tainted
-----------------------------
kernel/sched/core.c:7270 Illegal context switch in RCU-sched read-side critical section!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
7 locks held by syz-executor.1/9232:
 #0: ffffffff8b328c60 (console_lock){+.+.}-{0:0}, at: do_fb_ioctl+0x2e4/0x690 drivers/video/fbdev/core/fbmem.c:1106
 #1: ffff888041bd4078 (&fb_info->lock){+.+.}-{3:3}, at: lock_fb_info include/linux/fb.h:636 [inline]
 #1: ffff888041bd4078 (&fb_info->lock){+.+.}-{3:3}, at: do_fb_ioctl+0x2ee/0x690 drivers/video/fbdev/core/fbmem.c:1107
 #2: ffff888041adca78 (&helper->lock){+.+.}-{3:3}, at: drm_fb_helper_pan_display+0xce/0x970 drivers/gpu/drm/drm_fb_helper.c:1448
 #3: ffff8880159f01b8 (&dev->master_mutex){+.+.}-{3:3}, at: drm_master_internal_acquire+0x1d/0x70 drivers/gpu/drm/drm_auth.c:407
 #4: ffff888041adc898 (&client->modeset_mutex){+.+.}-{3:3}, at: drm_client_modeset_commit_locked+0x44/0x580 drivers/gpu/drm/drm_client_modeset.c:1143
 #5: ffffc90001c07730 (crtc_ww_class_acquire){+.+.}-{0:0}, at: drm_client_modeset_commit_atomic+0xb7/0x7c0 drivers/gpu/drm/drm_client_modeset.c:981
 #6: ffff888015986108 (crtc_ww_class_mutex){+.+.}-{3:3}, at: ww_mutex_lock_slow include/linux/ww_mutex.h:287 [inline]
 #6: ffff888015986108 (crtc_ww_class_mutex){+.+.}-{3:3}, at: modeset_lock+0x31c/0x650 drivers/gpu/drm/drm_modeset_lock.c:260

stack backtrace:
CPU: 1 PID: 9232 Comm: syz-executor.1 Not tainted 5.10.0-rc7-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:118
 ___might_sleep+0x25d/0x2b0 kernel/sched/core.c:7270
 __mutex_lock_common kernel/locking/mutex.c:935 [inline]
 __ww_mutex_lock.constprop.0+0xa9/0x2cc0 kernel/locking/mutex.c:1111
 ww_mutex_lock+0x3d/0x170 kernel/locking/mutex.c:1190
 modeset_lock+0x392/0x650 drivers/gpu/drm/drm_modeset_lock.c:263
 drm_modeset_lock drivers/gpu/drm/drm_modeset_lock.c:342 [inline]
 drm_modeset_lock+0x50/0x90 drivers/gpu/drm/drm_modeset_lock.c:338
 drm_atomic_get_plane_state+0x19d/0x510 drivers/gpu/drm/drm_atomic.c:481
 drm_client_modeset_commit_atomic+0x225/0x7c0 drivers/gpu/drm/drm_client_modeset.c:994
 drm_client_modeset_commit_locked+0x145/0x580 drivers/gpu/drm/drm_client_modeset.c:1145
 pan_display_atomic drivers/gpu/drm/drm_fb_helper.c:1395 [inline]
 drm_fb_helper_pan_display+0x28b/0x970 drivers/gpu/drm/drm_fb_helper.c:1455
 fb_pan_display+0x2f7/0x6c0 drivers/video/fbdev/core/fbmem.c:925
 fb_set_var+0x57f/0xda0 drivers/video/fbdev/core/fbmem.c:1043
 do_fb_ioctl+0x2f9/0x690 drivers/video/fbdev/core/fbmem.c:1108
 fb_compat_ioctl+0x17c/0xaf0 drivers/video/fbdev/core/fbmem.c:1315
 __do_compat_sys_ioctl+0x1d3/0x230 fs/ioctl.c:842
 do_syscall_32_irqs_on arch/x86/entry/common.c:78 [inline]
 __do_fast_syscall_32+0x56/0x80 arch/x86/entry/common.c:137
 do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:160
 entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
RIP: 0023:0xf7fd8549
Code: 03 74 c0 01 10 05 03 74 b8 01 10 06 03 74 b4 01 10 07 03 74 b0 01 10 08 03 74 d8 01 00 00 00 00 00 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f55d20bc EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000004601
RDX: 0000000020000240 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
detected fb_set_par error, error code: -16


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
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