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: Mon, 22 Nov 2010 08:35:41 -0500 From: Chris Metcalf <cmetcalf@...era.com> To: Cypher Wu <cypher.w@...il.com> CC: <linux-kernel@...r.kernel.org>, Américo Wang <xiyou.wangcong@...il.com>, Eric Dumazet <eric.dumazet@...il.com>, netdev <netdev@...r.kernel.org> Subject: Re: [PATCH] arch/tile: fix rwlock so would-be write lockers don't block new readers On 11/22/2010 12:39 AM, Cypher Wu wrote: > 2010/11/15 Chris Metcalf <cmetcalf@...era.com>: >> This avoids a deadlock in the IGMP code where one core gets a read >> lock, another core starts trying to get a write lock (thus blocking >> new readers), and then the first core tries to recursively re-acquire >> the read lock. >> >> We still try to preserve some degree of balance by giving priority >> to additional write lockers that come along while the lock is held >> for write, so they can all complete quickly and return the lock to >> the readers. >> >> Signed-off-by: Chris Metcalf <cmetcalf@...era.com> >> --- >> This should apply relatively cleanly to 2.6.26.7 source code too. >> [...] > > I've finished my business trip and tested that patch for more than an > hour and it works. The test is still running now. > > But it seems there still has a potential problem: we used ticket lock > for write_lock(), and if there are so many write_lock() occurred, is > 256 ticket enough for 64 or even more cores to avoiding overflow? > Since is we try to write_unlock() and there's already write_lock() > waiting we'll only adding current ticket. This is OK, since each core can issue at most one (blocking) write_lock(), and we have only 64 cores. Future >256 core machines will be based on TILE-Gx anyway, which doesn't have the 256-core limit since it doesn't use the spinlock_32.c implementation. -- Chris Metcalf, Tilera Corp. http://www.tilera.com -- 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
Powered by blists - more mailing lists