Re: [syzbot] [kernfs?] [usb?] WARNING in kernfs_get (5)

[syzbot <syzbot+2f44671e54488d20f0e6@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in firmware_uevent

============================================
WARNING: possible recursive locking detected
6.9.0-next-20240514-syzkaller-dirty #0 Not tainted
--------------------------------------------
kworker/0:2/930 is trying to acquire lock:
ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: firmware_uevent+0x2f/0x1a0 drivers/base/firmware_loader/sysfs.c:84

but task is already holding lock:
ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: fw_load_sysfs_fallback drivers/base/firmware_loader/fallback.c:123 [inline]
ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: fw_load_from_user_helper drivers/base/firmware_loader/fallback.c:164 [inline]
ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: firmware_fallback_sysfs+0x755/0x9d0 drivers/base/firmware_loader/fallback.c:240

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(fw_lock);
  lock(fw_lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

4 locks held by kworker/0:2/930:
 #0: ffff888015080948 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3206 [inline]
 #0: ffff888015080948 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x90a/0x1830 kernel/workqueue.c:3312
 #1: ffffc9000441fd00 ((work_completion)(&fw_work->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3207 [inline]
 #1: ffffc9000441fd00 ((work_completion)(&fw_work->work)){+.+.}-{0:0}, at: process_scheduled_works+0x945/0x1830 kernel/workqueue.c:3312
 #2: ffffffff8e1dd630 (umhelper_sem){++++}-{3:3}, at: usermodehelper_read_lock_wait+0x14e/0x260 kernel/umh.c:247
 #3: ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: fw_load_sysfs_fallback drivers/base/firmware_loader/fallback.c:123 [inline]
 #3: ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: fw_load_from_user_helper drivers/base/firmware_loader/fallback.c:164 [inline]
 #3: ffffffff8ec74268 (fw_lock){+.+.}-{3:3}, at: firmware_fallback_sysfs+0x755/0x9d0 drivers/base/firmware_loader/fallback.c:240

stack backtrace:
CPU: 0 PID: 930 Comm: kworker/0:2 Not tainted 6.9.0-next-20240514-syzkaller-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/02/2024
Workqueue: events request_firmware_work_func
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
 check_deadlock kernel/locking/lockdep.c:3062 [inline]
 validate_chain+0x15c1/0x58e0 kernel/locking/lockdep.c:3856
 __lock_acquire+0x1346/0x1fd0 kernel/locking/lockdep.c:5137
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5754
 __mutex_lock_common kernel/locking/mutex.c:608 [inline]
 __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
 firmware_uevent+0x2f/0x1a0 drivers/base/firmware_loader/sysfs.c:84
 dev_uevent+0x4e4/0x900 drivers/base/core.c:2687
 kobject_uevent_env+0x467/0x8e0 lib/kobject_uevent.c:558
 device_del+0x7db/0x9b0 drivers/base/core.c:3928
 fw_load_sysfs_fallback drivers/base/firmware_loader/fallback.c:125 [inline]
 fw_load_from_user_helper drivers/base/firmware_loader/fallback.c:164 [inline]
 firmware_fallback_sysfs+0x3a8/0x9d0 drivers/base/firmware_loader/fallback.c:240
 _request_firmware+0xcf5/0x12b0 drivers/base/firmware_loader/main.c:914
 request_firmware_work_func+0x12a/0x280 drivers/base/firmware_loader/main.c:1165
 process_one_work kernel/workqueue.c:3231 [inline]
 process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312
 worker_thread+0x86d/0xd70 kernel/workqueue.c:3393
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>


Tested on:

commit:         26dd54d0 Add linux-next specific files for 20240514
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git
console output: https://syzkaller.appspot.com/x/log.txt?x=157a1c84980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c8af44e051929224
dashboard link: https://syzkaller.appspot.com/bug?extid=2f44671e54488d20f0e6
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10776c68980000