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: Fri, 02 Dec 2011 10:05:15 +0100 From: Jens Axboe <axboe@...nel.dk> To: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com> CC: vgoyal@...hat.com, linux-kernel@...r.kernel.org Subject: Re: [patch]cfq-iosched: fix cfq_cic_link() race confition On 2011-12-02 09:05, Yasuaki Ishimatsu wrote: > cfq_cic_link() has race condition. When some processes which shared ioc > issue I/O to same block device simultaneously, cfq_cic_link() returns -EEXIST > sometimes. The race condition might stop I/O by following steps: > > step 1: Process A: Issue an I/O to /dev/sda > step 2: Process A: Get an ioc (iocA here) in get_io_context() which does not > linked with a cic for the device > step 3: Process A: Get a new cic for the device (cicA here) in > cfq_alloc_io_context() > > step 4: Process B: Issue an I/O to /dev/sda > step 5: Process B: Get iocA in get_io_context() since process A and B share the > same ioc > step 6: Process B: Get a new cic for the device (cicB here) in > cfq_alloc_io_context() since iocA has not been linked with a > cic for the device yet > > step 7: Process A: Link cicA to iocA in cfq_cic_link() > step 8: Process A: Dispatch I/O to driver and finish it > > step 9: Process B: Try to link cicB to iocA in cfq_cic_link() > But it fails with showing "cfq: cic link failed!" kernel > message, since iocA has already linked with cicA at step 7. > step 10: Process B: Wait for finishig I/O in get_request_wait() > The function does not wake up, when there is no I/O to the > device. > > When cfq_cic_link() returns -EEXIST, it means ioc has already linked with cic. > So when cfq_cic_link() return -EEXIST, retry cfq_cic_lookup(). Thanks, your analysis and fix looks correct. Good work! Applied. -- Jens Axboe -- 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