On Fri, Aug 1, 2014 at 9:21 PM, Jeff Layton <jlayton@xxxxxxxxxxxxxxx> wrote: > On Fri, 1 Aug 2014 07:50:53 +1000 > NeilBrown <neilb@xxxxxxx> wrote: > >> On Thu, 31 Jul 2014 14:20:07 -0700 Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote: >> >> > -----BEGIN PGP SIGNED MESSAGE----- >> > Hash: SHA1 >> > >> > On 07/31/2014 01:42 PM, NeilBrown wrote: >> > > On Thu, 31 Jul 2014 11:00:35 -0700 Ben Greear <greearb@xxxxxxxxxxxxxxx> wrote: >> > > >> > >> So, this has been asked all over the interweb for years and years, but the best answer I can find is to reboot the system or create a fake NFS server >> > >> somewhere with the same IP as the gone-away NFS server. >> > >> >> > >> The problem is: >> > >> >> > >> I have some mounts to an NFS server that no longer exists (crashed/powered down). >> > >> >> > >> I have some processes stuck trying to write to files open on these mounts. >> > >> >> > >> I want to kill the process and unmount. >> > >> >> > >> umount -l will make the mount go a way, sort of. But process is still hung. umount -f complains: umount2: Device or resource busy umount.nfs: /mnt/foo: >> > >> device is busy >> > >> >> > >> kill -9 does not work on process. >> > > >> > > Kill -1 should work (since about 2.6.25 or so). >> > >> > That is -[ONE], right? Assuming so, it did not work for me. >> >> No, it was "-9" .... sorry, I really shouldn't be let out without my proof >> reader. >> >> However the 'stack' is sufficient to see what is going on. >> >> The problem is that it is blocked inside the "VM" well away from NFS and >> there is no way for NFS to say "give up and go home". >> >> I'd suggest that is a bug. I cannot see any justification for fsync to not >> be killable. >> It wouldn't be too hard to create a patch to make it so. >> It would be a little harder to examine all call paths and create a >> convincing case that the patch was safe. >> It might be herculean task to convince others that it was the right thing >> to do.... so let's start with that one. >> >> Hi Linux-mm and fs-devel people. What do people think of making "fsync" and >> variants "KILLABLE" ?? >> >> I probably only need a little bit of encouragement to write a patch.... >> >> Thanks, >> NeilBrown >> > > > It would be good to fix this in some fashion once and for all, and the > wait_on_page_writeback wait is a major source of pain for a lot of > people. > > So to summarize... > > The problem in a nutshell is that Ben has some cached writes to the > NFS server, but the server has gone away (presumably forever). The > question is -- how do we communicate to the kernel that that server > isn't coming back and that those dirty pages should be invalidated so > that we can umount the filesystem? > > Allowing fsync/close to be killable sounds reasonable to me as at least > a partial solution. Both close(2) and fsync(2) are allowed to return > EINTR according to the POSIX spec. Allowing a kill -9 there seems > like it should be fine, and maybe we ought to even consider letting it > be susceptible to lesser signals. > > That still leaves some open questions though... > > Is that enough to fix it? You'd still have the dirty pages lingering > around, right? Would a umount -f presumably work at that point? 'umount -f' will kill any outstanding RPC calls that are causing the mount to hang, but doesn't do anything to change page states or NFS file/lock states. Cheers Trond -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>