pidns: Remove races by stopping the caching of proc_mnt
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From: Eric W. Biederman on 11 Jul 2010 10:30 Louis Rilling <Louis.Rilling(a)kerlabs.com> writes: > On 09/07/10 8:58 -0700, Eric W. Biederman wrote: >> >> Having proc reference the pid_namespace and the pid_namespace >> reference proc is a serious reference counting problem, which has >> resulted in both leaks and use after free problems. Mount already >> knows how to go from a pid_namespace to a mount of proc, so we don't >> need to cache the proc mount. >> >> To do this I introduce get_proc_mnt and replace pid_ns->proc_mnt users >> with it. Additionally I remove pid_ns_(prepare|release)_proc as they >> are now unneeded. >> >> This is slightly less efficient but it is much easier to avoid the >> races. If efficiency winds up being a problem we can revisit our data >> structures. > > IIUC, the difference between this solution and the first one I proposed is that > instead of pinning proc_mnt with mntget() at copy_process()-time, proc_mnt is > looked for and, if possible, mntget() at release_task()-time. > > Could you elaborate on the trade-off, that is accessing proc_mnt at > copy_process()-time vs looking up proc_mnt at release_task()-time? A little code simplicity. But Serge was right there is cost a noticeable cost. About 5%-7% more on lat_proc from lmbench. The real benefit was simplicity. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |