On Tuesday, July 07, 2015 04:38:26 PM Oliver Neukum wrote: > On Tue, 2015-07-07 at 16:32 +0200, Rafael J. Wysocki wrote: > > On Tuesday, July 07, 2015 03:16:48 PM Oliver Neukum wrote: > > > On Tue, 2015-07-07 at 14:14 +0200, Rafael J. Wysocki wrote: > > > > For example, on desktop systems I use user space syncs filesystems > > > > before > > > > writing to /sys/power/state, so the additional sys_sync() in the > > > > kernel doesn't > > > > seem to serve any purpose. > > > > > > There is a race you cannot close in user space. > > > > Yes, there is, but I'm not sure how much of a help the sync in the kernel > > provides here anyway. > > > > Say this happens. There is a process writing to a file running in parallel > > with the suspend process. Suspend starts and that process is frozen. The > > sync is called and causes all of the outstanding data to be written back. > > The user doesn't realize that the write is technically still in progress, so > > Well, in that case the user never got the feedback that the write is > finished. That is a race that always exists, like sending SIGKILL to a > running task. > What you describe is in principle unsolvable every time under > any circumstances. > > > he (or she) pulls the storage device out of the system, moves it to another > > system, makes changes (say removes the file written to by the process above, > > so the blocks previously occupied by that file are now used for some > > metadata) > > and moves the storage back to the suspended system. The system is resumed > > and the writing process continues writing possibly to the wrong blocks and > > corrupts the filesystem. > > That is a tough nut. But that's not a reason to make it worse. > I'd say there's no reason not to use a secondary interface to > suspend without syncing or to extend or introduce such an interface > if the API is deficient.
Well, the point here is that the sync we have doesn't prevent all potentially possible bad things from happening. It's a partial measure at best in that respect. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
