syzbot

BUG: using smp_processor_id() in preemptible [00000000] code: kworker/u4:4/181
caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
CPU: 1 PID: 181 Comm: kworker/u4:4 Not tainted 5.8.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: writeback wb_workfn (flush-8:0)
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 check_preemption_disabled+0x20d/0x220 lib/smp_processor_id.c:48
 ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
 ext4_ext_map_blocks+0x201b/0x33e0 fs/ext4/extents.c:4244
 ext4_map_blocks+0x4cb/0x1640 fs/ext4/inode.c:626
 mpage_map_one_extent fs/ext4/inode.c:2377 [inline]
 mpage_map_and_submit_extent fs/ext4/inode.c:2430 [inline]
 ext4_writepages+0x1a7b/0x33c0 fs/ext4/inode.c:2782
 do_writepages+0xfa/0x2a0 mm/page-writeback.c:2354
 __writeback_single_inode+0x12a/0x13d0 fs/fs-writeback.c:1452
 writeback_sb_inodes+0x515/0xdc0 fs/fs-writeback.c:1716
 __writeback_inodes_wb+0xc3/0x250 fs/fs-writeback.c:1785
 wb_writeback+0x8db/0xd50 fs/fs-writeback.c:1894
 wb_check_old_data_flush fs/fs-writeback.c:1996 [inline]
 wb_do_writeback fs/fs-writeback.c:2049 [inline]
 wb_workfn+0xab3/0x1090 fs/fs-writeback.c:2078
 process_one_work+0x965/0x1690 kernel/workqueue.c:2269
 worker_thread+0x96/0xe10 kernel/workqueue.c:2415
 kthread+0x3b5/0x4a0 kernel/kthread.c:291
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:293