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
| ||
|
Date: Thu, 11 Mar 2010 13:04:33 +0800 From: Miao Xie <miaox@...fujitsu.com> To: Paul Menage <menage@...gle.com> CC: David Rientjes <rientjes@...gle.com>, Lee Schermerhorn <lee.schermerhorn@...com>, Nick Piggin <npiggin@...e.de>, Linux-Kernel <linux-kernel@...r.kernel.org>, Linux-MM <linux-mm@...ck.org> Subject: Re: [PATCH 4/4] cpuset,mm: use rwlock to protect task->mempolicy and mems_allowed on 2010-3-10 3:42, Paul Menage wrote: > On Sat, Mar 6, 2010 at 6:33 PM, Miao Xie <miaox@...fujitsu.com> wrote: >> >> Before applying this patch, cpuset updates task->mems_allowed just like >> what you said. But the allocator is still likely to see an empty nodemask. >> This problem have been pointed out by Nick Piggin. >> >> The problem is following: >> The size of nodemask_t is greater than the size of long integer, so loading >> and storing of nodemask_t are not atomic operations. If task->mems_allowed >> don't intersect with new_mask, such as the first word of the mask is empty >> and only the first word of new_mask is not empty. When the allocator >> loads a word of the mask before >> >> current->mems_allowed |= new_mask; >> >> and then loads another word of the mask after >> >> current->mems_allowed = new_mask; >> >> the allocator gets an empty nodemask. > > Couldn't that be solved by having the reader read the nodemask twice > and compare them? In the normal case there's no race, so the second > read is straight from L1 cache and is very cheap. In the unlikely case > of a race, the reader would keep trying until it got two consistent > values in a row. I think this method can't fix the problem because we can guarantee the second read is after the update of mask completes. Thanks! Miao > > Paul > > > -- 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/
Powered by blists - more mailing lists