netdev - Re: [PATCH] net/core/sock.c remove extra wakeup

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] [day] [month] [year] [list]

Message-ID: <87prr027gy.fsf@basil.nowhere.org>
Date:	Sun, 01 Jun 2008 23:03:41 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Patrick Mullaney" <pmullaney@...ell.com>
Cc:	"Gregory Haskins" <GHaskins@...ell.com>, <davem@...emloft.net>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH] net/core/sock.c remove extra wakeup

"Patrick Mullaney" <pmullaney@...ell.com> writes:
>
> Would a better approach be?
>
> 1) clear the bit when the waiter returns(bottom of sock_wait_for_wmem)
> 2) add a new wait-queue to the socket to separate the writers
> 3) another idea?

A large reason this is tricky is because it is essentially lockless. So
alternative would be:

4) you add a spinlock which is always taken around the various condition
checks and bit manipulation. Not 100% sure if it would be bad to 
general SMP scalability (you would need to ensure that the bouncing
lock cache line isn't a performance problem), but at least it would 
be much safer and makes it much easier to verify your change is correct.

Actually the wait queue already has such a lock, so it might not be
that expensive if you switch the wait queue to a lockless version.

-Andi

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html