linux-kernel - Re: oops in file

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Date:	Thu, 23 Oct 2008 12:46:01 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Manish Lachwani <mlachwani@...il.com>
cc:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: oops in file_storage.c

On Thu, 23 Oct 2008, Manish Lachwani wrote:

> Hi Alan,
> 
> >
> > Hmm.  On my system (2.6.27) the code has moved to fs/sync.c/do_fsync(),
> > and it has changed a fair amount.  Maybe file_storage.c should be
> > changed to match.
> 
> I have the latest git checkout of
> http://www.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
> and it seems that do_fsync() is still quite similar to fsync_sub().
> Also, I checked older trees like 2.6.22 and do_fsync() is still in
> fs/sync.c

That just goes to show how old file_storage.c is.

> > In fact, the easiest approach would be to EXPORT do_fsync() and then
> > call it directly.  I don't know whether people would like this, though.
> >
> 
> I could try this. But I don't see much difference b/w do_fsync() and
> fsync_sub(). However in do_fsync(), filemap_fdatawrite() is called
> before the mutex_lock() and filemap_fdatawait() is called after the
> mutex_unlock().
> 
> Here is do_fsync() -
> 
> long do_fsync(struct file *file, int datasync)
> {
>         int ret;
>         int err;
>         struct address_space *mapping = file->f_mapping;

file_storage does

		inode = filp->f_path.dentry->d_inode;

instead, and uses inode in place of mapping->host and inode->i_mapping 
in place of mapping.  Should this be changed?  I have no idea, beyond 
feeling that the core kernel code has got to be more up-to-date.  Same 
goes for the ordering of the locks and the filemap_* calls.

>         if (!file->f_op || !file->f_op->fsync) {
>                 /* Why?  We can still call filemap_fdatawrite */
>                 ret = -EINVAL;
>                 goto out;
>         }
> 
>         ret = filemap_fdatawrite(mapping);
> 
>         /*
>          * We need to protect against concurrent writers, which could cause
>          * livelocks in fsync_buffers_list().
>          */
>         mutex_lock(&mapping->host->i_mutex);
>         err = file->f_op->fsync(file, file->f_path.dentry, datasync);
>         if (!ret)
>                 ret = err;
>         mutex_unlock(&mapping->host->i_mutex);
>         err = filemap_fdatawait(mapping);
>         if (!ret)
>                 ret = err;
> out:
>         return ret;
> }

If the EXPORT route is acceptable, I'd prefer to use it.

Alan Stern

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