linux-kernel - Re: [PATCH 2/2] lockdep: check that no locks held at freeze time

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 for Android: free password hash cracker in your pocket

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

Date:	Sat, 4 May 2013 17:23:01 -0700
From:	Colin Cross <ccross@...roid.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm@...l.org>, lkml <linux-kernel@...r.kernel.org>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mandeep Singh Baines <msb@...omium.org>,
	Paul Walmsley <paul@...an.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-nfs@...r.kernel.org,
	Linux PM list <linux-pm@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Ben Chan <benchan@...omium.org>
Subject: Re: [PATCH 2/2] lockdep: check that no locks held at freeze time

On Sat, May 4, 2013 at 5:05 PM, Pavel Machek <pavel@....cz> wrote:
> Hi!
>
>> >> >> --- a/kernel/exit.c
>> >> >> +++ b/kernel/exit.c
>> >> >> @@ -835,7 +835,7 @@ void do_exit(long code)
>> >> >>       /*
>> >> >>        * Make sure we are holding no locks:
>> >> >>        */
>> >> >> -     debug_check_no_locks_held(tsk);
>> >> >> +     debug_check_no_locks_held();
>> >> >
>> >> > Is task guaranteed == current?
>> >>
>> >> Yes, the first line of do_exit is:
>> >>         struct task_struct *tsk = current;
>> >
>> > Aha, I understand it now.
>> >
>> > Accessing current is slower than local variable. So your "new" code
>> > will work but will be slower. Please revert this part.
>>
>> Using current instead of passing in tsk was done at Andrew Morton's
>> suggestion, and makes no difference from the freezer's perspective
>> since it would have to use current to get the task to pass in, so I'm
>> going to leave it as is.
>
> Well, current is:
>
> static inline struct thread_info *current_thread_info(void)
> {
>         register unsigned long sp asm ("sp");
>         return (struct thread_info *)(sp & ~(THREAD_SIZE - 1));
> }
>
> #define get_current() (current_thread_info()->task)
>
> #define current get_current()
>
> Instead of passing computed value to debug_check_no_locks_held(), you
> force it to be computed again. do_exit() performance matters for
> configure scripts, etc.
>
> I'd say it makes sense to keep the optimalization. akpm can correct
> me.

That translates to 3 instructions, with no memory accesses:
c0008350:       e1a0300d        mov     r3, sp
c0008354:       e3c32d7f        bic     r2, r3, #8128   ; 0x1fc0
c0008358:       e3c2203f        bic     r2, r2, #63     ; 0x3f
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/