> Now, nfs_flush_pages() may return NULL in two cases:
>
> a) no write request is pending. Fine.
>
> b) the write-back request is already in progress. BAD.
>
> b) means that whenever the write back request already has been
> triggered the system might be caught in a loop. This happens because
> the nfs-write-back request might sleep while waiting for the
> nfs-server to answer. But as nfs_flush_pages() returns NULL in this
> case the function nfs_flush_dirty_pages() not wait and return
> immediately to its caller nfs_dentry_iput().
Hi Claus,
Thanks for your good detective work! The nfs_flush_dirty_pages() is
indeed supposed to wait until all requests are finished, which is why
nfs_dentry_iput() uses it. (The iput can't proceed until all requests
are finished, as the requests need information in the dentry and the
dentry may disappear soon.)
> The following patch maybe fixes the problem. It changes
> nfs_flush_pages() to also return the write-back requests to its caller
> if the write back request already is in progress. Maybe this has side
> effects?
I'll look through the code look for other side effects. I've recently
added a NFS_WRITE_COMPLETE flag set in the nfs writeback callback to
watch out for other problems when flushing requests.
Regards,
Bill