From: Hydro Flask <hydroflask@yqxmail.com>
To: musl@lists.openwall.com
Subject: Re: [musl] Potential deadlock in pthread_kill()
Date: Mon, 06 Jul 2020 15:37:47 -0700 [thread overview]
Message-ID: <5144617df2c8010b62813b5ed2c0dfef@yqxmail.com> (raw)
In-Reply-To: <20200706222202.GN6430@brightrain.aerifal.cx>
On 2020-07-06 15:22, Rich Felker wrote:
> On Mon, Jul 06, 2020 at 03:14:43PM -0700, Hydro Flask wrote:
>> On 2020-07-06 15:00, Rich Felker wrote:
>> >Yes, I see it clearly now. Sorry it took a while. I have prepared the
>> >attached patch which I'll push soon if there are no problems.
>>
>> Needs one more tiny tweak. I noticed that pthread_cancel() calls
>> pthread_kill(). That means pthread_kill() must be async-cancel-safe.
>> If an asynchronous cancellation happens after pthread_kill() grabs
>> the killlock, then it will deadlock because the asynchronous
>> pthread_exit(PTHREAD_CANCELED) call will then recursively try to
>> grab killlock.
>>
>> The solution as far as I can tell is to not just block app signals
>> when grabbing killlock, but all signals.
>
> Are you in agreement that it suffices for only pthread_kill to block
> all signals? (Still blocking just app signals everywhere else) The
> scheduling functions could be changed too, but I'm hesitant to change
> pthread_exit without thinking about it further since it has a lot more
> subtleties. And I think only pthread_kill needs it since it's the only
> one that needs to be AC-safe.
Yes I think that's right, since every other function that grabs the
killlock can assume that async cancellation won't happen.
prev parent reply other threads:[~2020-07-06 22:38 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-30 4:19 Hydro Flask
2020-06-30 4:43 ` Rich Felker
2020-06-30 6:19 ` Hydro Flask
2020-06-30 9:26 ` Rich Felker
2020-06-30 14:58 ` Markus Wichmann
2020-06-30 16:28 ` Hydro Flask
2020-06-30 19:28 ` Dmitry Samersoff
2020-06-30 19:54 ` Rich Felker
2020-06-30 21:00 ` Hydro Flask
2020-07-06 22:00 ` Rich Felker
2020-07-06 22:14 ` Hydro Flask
2020-07-06 22:22 ` Rich Felker
2020-07-06 22:37 ` Hydro Flask [this message]
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