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SubjectRe: [RFC PATCH 1/6] x86/alternative: assert text_mutex is taken
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at 10:11 AM, Nadav Amit <namit@vmware.com> wrote:

> at 1:59 AM, Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
>> On Wed, 29 Aug 2018 01:11:42 -0700
>> Nadav Amit <namit@vmware.com> wrote:
>>
>>> Use lockdep to ensure that text_mutex is taken when text_poke() is
>>> called.
>>>
>>> Actually it is not always taken, specifically when it is called by kgdb,
>>> so take the lock in these cases.
>>
>> Can we really take a mutex in kgdb context?
>>
>> kgdb_arch_remove_breakpoint
>> <- dbg_deactivate_sw_breakpoints
>> <- kgdb_reenter_check
>> <- kgdb_handle_exception
>> <- __kgdb_notify
>> <- kgdb_ll_trap
>> <- do_int3
>> <- kgdb_notify
>> <- die notifier
>>
>> kgdb_arch_set_breakpoint
>> <- dbg_activate_sw_breakpoints
>> <- kgdb_reenter_check
>> <- kgdb_handle_exception
>> ...
>>
>> Both seems called in exception context, so we can not take a mutex lock.
>> I think kgdb needs a special path.
>
> You are correct, but I don’t want a special path. Presumably text_mutex is
> guaranteed not to be taken according to the code.
>
> So I guess the only concern is lockdep. Do you see any problem if I change
> mutex_lock() into mutex_trylock()? It should always succeed, and I can add a
> warning and a failure path if it fails for some reason.

Err.. This will not work. I think I will drop this patch, since I cannot
find a proper yet simple assertion. Creating special path just for the
assertion seems wrong.
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