linux-kernel - Re: [tip:locking/core] sched/wait: Fix signal handling in bit wait helpers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87si3bpaxy.fsf@notabene.neil.brown.name>
Date:	Thu, 10 Dec 2015 08:30:01 +1100
From:	NeilBrown <nfbrown@...ell.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	torvalds@...ux-foundation.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, efault@....de, mingo@...nel.org,
	hpa@...or.com, vladimir.murzin@....com,
	linux-tip-commits@...r.kernel.org, jstancek@...hat.com,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [tip:locking/core] sched/wait: Fix signal handling in bit wait helpers

On Wed, Dec 09 2015, Peter Zijlstra wrote:

> On Wed, Dec 09, 2015 at 12:06:33PM +1100, NeilBrown wrote:
>> On Tue, Dec 08 2015, Peter Zijlstra wrote:
>> 
>> >>  
>> >
>> > *sigh*, so that patch was broken.. the below might fix it, but please
>> > someone look at it, I seem to have a less than stellar track record
>> > here...
>> 
>> This new change seems to be more intrusive than should be needed.
>> Can't we just do:
>> 
>> 
>>  __sched int bit_wait(struct wait_bit_key *word)
>>  {
>> +	long state = current->state;
>
> No, current->state can already be changed by this time.

Does that matter?
It can only have changed to TASK_RUNNING - right?
In that case signal_pending_state() will return 0 and the bit_wait() acts
as though the thread was woken up normally (which it was) rather than by
a signal (which maybe it was too, but maybe that happened just a tiny
bit later).

As long as signal delivery doesn't change ->state, we should be safe.
We should even be safe testing ->state *after* the call the schedule().

NeilBrown

Download attachment "signature.asc" of type "application/pgp-signature" (819 bytes)