Re: [PATCH v1] kdb: Fix the deadlock issue in KDB debugging.

Daniel Thompson
2024-03-20T16:28:06Z

^^^ This is v2 isn't it?

On Sat, Mar 16, 2024 at 10:34:43AM +0800, liu.yec@h3c.com wrote:
> From: LiuYe <liu.yeC@h3c.com>
>
> Currently, if CONFIG_KDB_KEYBOARD is enabled, then kgdboc will
> attempt to use schedule_work() to provoke a keyboard reset when transitioning out

Please format the description correctly.

> of the debugger and back to normal operation. This can cause
> deadlock because schedule_work() is not NMI-safe.

Wasn't there another paragraph to go here?

: The stack trace below shows an example of the problem. In this
: case the master cpu is not running from NMI but it has parked
: the slave CPUs using an NMI and the parked CPUs is holding
: spinlocks needed by schedule_work().

> example:
> BUG: spinlock lockup suspected on CPU#0, namex/10450
> lock: 0xffff881ffe823980, .magic: dead4ead, .owner: namexx/21888, .owner_cpu: 1
> ffff881741d00000 ffff881741c01000 0000000000000000 0000000000000000
> ffff881740f58e78 ffff881741cffdd0 ffffffff8147a7fc ffff881740f58f20
> Call Trace:
> [<ffffffff81479e6d>] ? __schedule+0x16d/0xac0
> [<ffffffff8147a7fc>] ? schedule+0x3c/0x90
> [<ffffffff8147e71a>] ? schedule_hrtimeout_range_clock+0x10a/0x120
> [<ffffffff8147d22e>] ? mutex_unlock+0xe/0x10
> [<ffffffff811c839b>] ? ep_scan_ready_list+0x1db/0x1e0
> [<ffffffff8147e743>] ? schedule_hrtimeout_range+0x13/0x20
> [<ffffffff811c864a>] ? ep_poll+0x27a/0x3b0
> [<ffffffff8108c540>] ? wake_up_q+0x70/0x70
> [<ffffffff811c99a8>] ? SyS_epoll_wait+0xb8/0xd0
> [<ffffffff8147f296>] ? entry_SYSCALL_64_fastpath+0x12/0x75
> CPU: 0 PID: 10450 Comm: namex Tainted: G O 4.4.65 #1
> Hardware name: Insyde Purley/Type2 - Board Product Name1, BIOS 05.21.51.0036 07/19/2019
> 0000000000000000 ffff881ffe813c10 ffffffff8124e883 ffff881741c01000
> ffff881ffe823980 ffff881ffe813c38 ffffffff810a7f7f ffff881ffe823980
> 000000007d2b7cd0 0000000000000001 ffff881ffe813c68 ffffffff810a80e0
> Call Trace:
> <#DB> [<ffffffff8124e883>] dump_stack+0x85/0xc2
> [<ffffffff810a7f7f>] spin_dump+0x7f/0x100
> [<ffffffff810a80e0>] do_raw_spin_lock+0xa0/0x150
> [<ffffffff8147eb55>] _raw_spin_lock+0x15/0x20
> [<ffffffff8108c256>] try_to_wake_up+0x176/0x3d0
> [<ffffffff8108c4c5>] wake_up_process+0x15/0x20
> [<ffffffff8107b371>] insert_work+0x81/0xc0
> [<ffffffff8107b4e5>] __queue_work+0x135/0x390
> [<ffffffff8107b786>] queue_work_on+0x46/0x90
> [<ffffffff81313d28>] kgdboc_post_exp_handler+0x48/0x70
> [<ffffffff810ed488>] kgdb_cpu_enter+0x598/0x610
> [<ffffffff810ed6e2>] kgdb_handle_exception+0xf2/0x1f0
> [<ffffffff81054e21>] __kgdb_notify+0x71/0xd0
> [<ffffffff81054eb5>] kgdb_notify+0x35/0x70
> [<ffffffff81082e6a>] notifier_call_chain+0x4a/0x70
> [<ffffffff8108304d>] notify_die+0x3d/0x50
> [<ffffffff81017219>] do_int3+0x89/0x120
> [<ffffffff81480fb4>] int3+0x44/0x80
>
> Suggested-by: daniel.thompson@linaro.org

Thanks for the credit but I think the following is probably a better way
to express it:

Co-authored-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>

Daniel.