[CHECKER] inconsistent NFS stat cache (NFS on ext3, 2.6.11)

[Junfeng Yang]

Hi,

We checked NFS on top of ext3 using FiSC (our file system model checker)
and found a case where NFS stat cache can contain inconsistent entries.

Basically, to trigger this inconsistency, just do the following steps:
1. create a file A1, write a few bytes to it, so A1 is 4 words
2. create a hard link A2, pointing to A1
3. stat on A2. A2's size is 4 words
4. truncate A1 to a larger size, write a few bytes at the end. now it's
1031 words.
5. stat on A2. it's size is still 4 words, which should be 1031 words

We have a test case to re-create this warning.  You can download it at
http://fisc.stanford.edu/bug16/crash.c.  It includes some sudo commands
to mount nfs partitions, which you might want to change according to your
local settings.

cat /etc/exports shows:
/mnt/sbd0-export          localhost(rw,sync)
/mnt/sbd1-export          localhost(rw,sync)

Let me know if you have any problems reproducing the warning. We'd
appreciate any confirmations/clarifications.

-Junfeng

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