loop: WARNING in sysfs_remove_group

[Dmitry Vyukov]

Hello,

I've got the following WARNING while running syzkaller on
093b995e3b55a0ae0670226ddfcb05bfbf0099ae. Note the preceding injected
kmalloc failure, most likely it's the root cause.

FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 3 PID: 21172 Comm: syz-executor4 Not tainted 4.11.0-rc3+ #364
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x1b8/0x28d lib/dump_stack.c:52
 fail_dump lib/fault-inject.c:45 [inline]
 should_fail+0x78a/0x870 lib/fault-inject.c:154
 should_failslab+0xec/0x120 mm/failslab.c:31
 slab_pre_alloc_hook mm/slab.h:434 [inline]
 slab_alloc mm/slab.c:3394 [inline]
 kmem_cache_alloc+0x200/0x720 mm/slab.c:3570
 kmem_cache_zalloc include/linux/slab.h:653 [inline]
 __kernfs_new_node+0xd1/0x430 fs/kernfs/dir.c:629
 kernfs_new_node+0x80/0xf0 fs/kernfs/dir.c:661
 kernfs_create_dir_ns+0x41/0x140 fs/kernfs/dir.c:933
 kernfs_create_dir include/linux/kernfs.h:477 [inline]
 internal_create_group+0xf7/0x8f0 fs/sysfs/group.c:124
 sysfs_create_group+0x1f/0x30 fs/sysfs/group.c:156
 loop_sysfs_init drivers/block/loop.c:802 [inline]
 loop_set_fd drivers/block/loop.c:940 [inline]
 lo_ioctl+0xbbf/0x1670 drivers/block/loop.c:1341
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0xcf6/0x1f80 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1978
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f8df2ef7858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000000000006 RSI: 0000000000004c00 RDI: 0000000000000005
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007f8df2ef7618 R15: 00007f8df2ef7788
------------[ cut here ]------------
WARNING: CPU: 0 PID: 21188 at fs/sysfs/group.c:237
sysfs_remove_group+0x167/0x1c0 fs/sysfs/group.c:235
sysfs group 'loop' not found for kobject 'loop6'
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 21188 Comm: syz-executor4 Not tainted 4.11.0-rc3+ #364
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x1b8/0x28d lib/dump_stack.c:52
 panic+0x20c/0x423 kernel/panic.c:180
 __warn+0x1c4/0x1e0 kernel/panic.c:541
 warn_slowpath_fmt+0xc1/0x100 kernel/panic.c:564
 sysfs_remove_group+0x167/0x1c0 fs/sysfs/group.c:235
 loop_sysfs_exit drivers/block/loop.c:808 [inline]
 loop_clr_fd+0x46d/0xa90 drivers/block/loop.c:1055
 lo_ioctl+0x1dc/0x1670 drivers/block/loop.c:1348
 __blkdev_driver_ioctl block/ioctl.c:297 [inline]
 blkdev_ioctl+0xcf6/0x1f80 block/ioctl.c:594
 block_ioctl+0xde/0x120 fs/block_dev.c:1978
 vfs_ioctl fs/ioctl.c:45 [inline]
 do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
 SYSC_ioctl fs/ioctl.c:700 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
 entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f8df2ed6858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000007080a8 RCX: 0000000000445b79
RDX: 0000000000000000 RSI: 0000000000004c01 RDI: 0000000000000005
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f8df2ed79c0 R15: 00007f8df2ed7700