On Wed, 2018-05-30 at 00:38 +0000, Shawn Lu (shawlu) wrote: > Dear Maintainers of NFS: > > I need help to better understand behavior of “-f” option > for “umount” NFS file system. Here is what I got from Man page > ( https://linux.die.net/man/8/umount) : > > “ -f Force unmount (in case of an unreachable NFS system). (Requires > kernel 2.1.116 or later.)” > > My interpretation of Man page is “umount –f” should able to force > umount nfs when NFS server is not available. > > On my test, I am observed “umount –f” is not always work as > expected. Also there some behavior difference on “umount –f “ with > regarding to different NFS version. > Here is my experiment on 4.4 Kernel ( I am believe this is true for > latest kernel): > Test for nfsv3: > a) From Host A, Start NFS server and export “/shared” directory > ,which has only my file test.txt > b) from Host B, remote mount host A:/shared to /test using > nfsv3 > c) from host B open file /test/test.txt > d) from host B, do “umount –f /test“, it returns “device is busy” > e) From host A , do following “rm -f /etc/exports ; touch > /etc/exports ; exportfs -ra” > f) From host B , do “umount –f /test“, it returns “device is > busy” > g) Reboot HOST A > h) From host B: do “umount –f /test“ succeed. > > Test for nfsv4: > i) From Host A, Start NFS server and export “/shared” > directory ,which has only my file test.txt > j) from Host B, remote mount host A:/shared > to /test using nfsv4 > k) from host B open file /test/test.txt > l) from host B, do “umount –f /test“, it returns “device > is busy” > m) From host A , do following “rm -f /etc/exports ; touch > /etc/exports ; exportfs -ra” > n) From host B , do “umount –f /test“, it returns > “device is busy” > o) Reboot NFS server( HOST A) > p) From host B: do “umount –f /test“ , still return > “device is busy” > > > For both nfsv3 and nfsv4, “umount –f “ will fails even the super > block is already “staled”(check step f and step n) . “-f” option for > NFSv4 is more “broken” since now it will not succeed even with NFS > server off line. > > Here my questions: > 1. If “umount –f “ can’t force unmount “staled ” nfs mount , How > it differential itself from regular umount (without –f)? > 2. is “-f” option is “broken” for NFSv4 or it is intend behavior to > fail “umount –f” even Server is offline ? I'm not an NFS maintainer, but I had a very similar question a few months ago and even wrote some patches to try and get a more "forceful" unmount. Unfortunately, I got distracted with other tasks and haven't looped around to finish the job. You can read through the lengthy discussion and patches here: Initial Discussion: https://www.spinics.net/lists/linux-nfs/msg66073.html RFC Patches: https://www.spinics.net/lists/linux-nfs/msg66348.html https://www.spinics.net/lists/linux-nfs/msg66421.html https://www.spinics.net/lists/linux-nfs/msg66466.html https://www.spinics.net/lists/linux-nfs/msg66483.html Hopefully, that helps. If you are interested in reviving this work, I am still interested and would be willing to help out. > > Really appreciate if someone in the mailing list can help to answer > my dumb questions. > > > Thanks, > Shawn > > > > > > > NrybXǧv^){.n+{"^nrzh& Gh(階ݢj"mzޖfh~m -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
