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SubjectRe: strange sparc64 -> i586 intermittent but reproducible NFS write errors to one and only one fs
[Large amount of quoting to provide useful context; see below.]

On Fri, 10 Jan 2003, Denis Vlasenko recommended:
> On 10 January 2003 00:56, Nix wrote:
>> When I rebooted my systems into 2.4.20 (from 2.4.19), I started
>> seeing EIO write() errors to files in my ext3 home directory
>> (NFS-mounted, exported async).
>> So I knocked up a test program (included below) to try to track the
>> failing writes down, and got more confused.
>> The properties of the failing writes that I've been able to determine
>> thus far are as follows; look out, they're weird as hell:
>> - the failures are definitely from write(), not open().
>> - writes from sparc64 to one filesystem, and only one filesystem, on
>> i586, both running 2.4.20, UDP NFSv3; rquotad and quotas are on,
>> but I am well within my quota. (quota 3.06, nfs-utils 1.0). Writes to
>> other filesystems on the same machine, even if they too are using
>> ext3, even if they too have user quotas for the same user.
>> What differs between filesystems that work and the one that fails
>> I can't tell; other FSen *on the same block device* work... (the
>> block device is an un-RAIDed SCSI disk.)
>> - local writes to the same filesystem, with the same test program,
>> never fail.
>> - writes from another IA32 box (all these boxes are near-clones of
>> each other as far as software is concerned) to the NFS server box
>> never fail.
>> - It happens if I mount the fs with -o soft (my default for all NFS
>> mounts for robustness-in-the-presence-of-machine-failure reasons),
>> but also if I mount with -o hard :(( besides, the timeouts happen
>> far too fast for it to be major timeout expiry that casues the EIOs.
>> - The failure always occurs for writes that cross the 2^21 byte
>> boundary, but not all such writes fail. You seem to need to have
>> done a lot of write()s before, perhaps even starting with O_TRUNC
>> and write()ing like mad from there on up (the WRITES_PER_OPEN
>> #define is a way to test that; I've never had a failure for a file
>> opened with O_APPEND, even if it crossed the 2^21 byte boundary).
>> - It happens whether _LARGEFILE_SOURCE / _FILE_OFFSET_BITS are
>> defined or not (I'd be amazed if this affected it, actually, but
>> it never hurts to check).
>> - Despite the EIO, the write actually *succeeds* most of the time
>> (perhaps not all the time; again, I'm not sure yet). In fact...
>> - It is quite thoroughly inconsistent. If you #define REPRODUCE to 1
>> in the test program and fill out sizes_to_reproduce[] with a set
>> of write() sizes that have caused the error in the past, the error
>> happens again, but not always:

[and more; see <>;
note that I have seen errors on writes to files of total size <2Mb --- e.g.,
my mail overview databases --- but I can't reproduce them with a test program

> This beast is most probably Sparc64 or 64-bit arch specific.

That seems very likely.

> Try to pin down the first 2.4.20-preN where it appears.
> Then inform NFS and Sparc64 folks.

Done. Sorry for the delay; this box is quite hard to arrange to reboot :(

Anyway, the problem appears in 2.4.20-pre10; I suspect

Trond Myklebust <>:
o Workaround NFS hangs introduced in 2.4.20-pre

(so Cc:ed)

Does anyone have a pointer to this patch so I can try reversing it from
2.4.20pre10? (I can't see it on l-k, but since I don't know what it
looks like it's hard to find it in the archives; I don't have bitkeeper
on this machine, and can't, as one of my current projects involves
version-control filesystems).

Anyone got any other ideas, suggestions, or anything?


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