[Bug libc/12552] New: lstat hangs when trying to stat a file being written to via nfs

["cade.robinson at gmail dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=12552

           Summary: lstat hangs when trying to stat a file being written
                    to via nfs
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: drepper.fsp@gmail.com
        ReportedBy: cade.robinson@gmail.com


I don't know if this is libc or kernel but I am starting here.

lstat hangs for a few seconds when trying to stat a file being written to via
NFS.

I have tested this with glibc 2.4 (SLES 10), 2.11 (SLES 11, ubuntu 10.04), 2.12
(ubuntu 10.10),  and 2.13 (arch).
I have tested against a Netapp filer and an ubuntu 7.10 NFS server.

SLES9 with glibc 2.3.3 does not exhibit this behavior.


Steps to recreate:
Open two windows to a client mounting something NFS and change to the NFS
mount.
Run in one window:
dd if=/dev/zero of=testfile bs=1024 count=10240000

In the other window run this while the dd is running:
strace stat testfile
or 
strace ls testfile
The strace will hang for a bit on the lstat() system call on the NFS client
that is running the dd (or write).

If you run the strace command on another client at the same time the dd is
running you will get no pause/hang with lstat.

I can see this with anything that runs lstat like ls, stat, a compiled program
that just does an lstat, etc.

Again I don't know if this is glibc or the kernel but I don't know where to
start and this is killing us performance wise.

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