linux-next test error: BUG: using smp_processor_id() in preemptible [ADDR] code: syz-fuzzer/6793

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    48f99181 Add linux-next specific files for 20200603
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1006bca6100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=365f706273eaf502
dashboard link: https://syzkaller.appspot.com/bug?extid=878f276b4892a4438f95
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+878f276b4892a4438f95@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: using smp_processor_id() in preemptible [00000000] code: syz-fuzzer/6793
caller is ext4_mb_new_blocks+0xa4d/0x3b70 fs/ext4/mballoc.c:4711
CPU: 1 PID: 6793 Comm: syz-fuzzer Not tainted 5.7.0-next-20200603-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: 0033:0x4b02a0
Code: Bad RIP value.
RSP: 002b:000000c00004f4b8 EFLAGS: 00000212 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 000000c00002c000 RCX: 00000000004b02a0
RDX: 00000000000001c0 RSI: 000000c000026960 RDI: ffffffffffffff9c
RBP: 000000c00004f510 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: ffffffffffffffff
R13: 000000000000004c R14: 000000000000004b R15: 0000000000000100


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