linux-next test error: BUG: using smp_processor_id() in preemptible code in ext4_mb_new_blocks

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    af30725c Add linux-next specific files for 20200605
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=126f99a6100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=579d800cf0c74ef
dashboard link: https://syzkaller.appspot.com/bug?extid=f72682b02970a74a7858
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+f72682b02970a74a7858@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: using smp_processor_id() in preemptible [00000000] code: systemd-rfkill/6769
caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
CPU: 1 PID: 6769 Comm: systemd-rfkill Not tainted 5.7.0-next-20200605-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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
 ext4_getblk+0xad/0x520 fs/ext4/inode.c:833
 ext4_bread+0x7c/0x380 fs/ext4/inode.c:883
 ext4_append+0x153/0x360 fs/ext4/namei.c:67
 ext4_init_new_dir fs/ext4/namei.c:2757 [inline]
 ext4_mkdir+0x5e0/0xdf0 fs/ext4/namei.c:2802
 vfs_mkdir+0x419/0x690 fs/namei.c:3632
 do_mkdirat+0x21e/0x280 fs/namei.c:3655
 do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f6d60012687
Code: Bad RIP value.
RSP: 002b:00007ffd286d9ca8 EFLAGS: 00000246 ORIG_RAX: 0000000000000053
RAX: ffffffffffffffda RBX: 000055f82bd8d985 RCX: 00007f6d60012687
RDX: 00007ffd286d9b70 RSI: 00000000000001ed RDI: 000055f82bd8d985
RBP: 00007f6d60012680 R08: 0000000000000100 R09: 0000000000000000
R10: 000055f82bd8d980 R11: 0000000000000246 R12: 00000000000001ed
R13: 00007ffd286d9e30 R14: 0000000000000000 R15: 0000000000000000


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