BUG: sleeping function called from invalid context in __kmalloc

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    90568ecf Merge tag 'kvm-5.6-2' of git://git.kernel.org/pub..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=107413bee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=69fa012479f9a62
dashboard link: https://syzkaller.appspot.com/bug?extid=98704a51af8e3d9425a9
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+98704a51af8e3d9425a9@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: sleeping function called from invalid context at mm/slab.h:565
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 12445, name: syz-executor.1
1 lock held by syz-executor.1/12445:
 #0: ffffffff89310218 (sb_lock){+.+.}, at: spin_lock include/linux/spinlock.h:338 [inline]
 #0: ffffffff89310218 (sb_lock){+.+.}, at: sget_fc+0xdc/0x640 fs/super.c:521
Preemption disabled at:
[<ffffffff81be818c>] spin_lock include/linux/spinlock.h:338 [inline]
[<ffffffff81be818c>] sget_fc+0xdc/0x640 fs/super.c:521
CPU: 0 PID: 12445 Comm: syz-executor.1 Not tainted 5.5.0-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+0x1fb/0x318 lib/dump_stack.c:118
 ___might_sleep+0x449/0x5e0 kernel/sched/core.c:6800
 __might_sleep+0x8f/0x100 kernel/sched/core.c:6753
 slab_pre_alloc_hook mm/slab.h:565 [inline]
 slab_alloc mm/slab.c:3306 [inline]
 __do_kmalloc mm/slab.c:3654 [inline]
 __kmalloc+0x6f/0x340 mm/slab.c:3665
 kmalloc include/linux/slab.h:560 [inline]
 path_remove_extra_slash+0xae/0x2a0 fs/ceph/super.c:495
 compare_mount_options fs/ceph/super.c:553 [inline]
 ceph_compare_super+0x1d4/0x560 fs/ceph/super.c:1052
 sget_fc+0x139/0x640 fs/super.c:524
 ceph_get_tree+0x467/0x1540 fs/ceph/super.c:1127
 vfs_get_tree+0x8b/0x2a0 fs/super.c:1547
 do_new_mount fs/namespace.c:2822 [inline]
 do_mount+0x18ee/0x25a0 fs/namespace.c:3142
 __do_sys_mount fs/namespace.c:3351 [inline]
 __se_sys_mount+0xdd/0x110 fs/namespace.c:3328
 __x64_sys_mount+0xbf/0xd0 fs/namespace.c:3328
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45b399
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f77dba0ec78 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f77dba0f6d4 RCX: 000000000045b399
RDX: 0000000020000140 RSI: 00000000200000c0 RDI: 0000000020000040
RBP: 000000000075c070 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000745 R14: 00000000004c8c38 R15: 000000000075c07c
ceph: No mds server is up or the cluster is laggy


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