Need of inode->i_mutex in xfs_write()

Need of inode->i_mutex in xfs_write()

[kanishk rastogi]

I was looking at the xfs_write code path in kernel 2.6.20 .......
I saw it acquiring inode->i_mutex .
Whats the need ?
What are we safegaurding inode for.

AFAIK its used for protecting the incode inode. (CMIIW)

regards
kanishk

Re: Need of inode->i_mutex in xfs_write()

[David Chinner]

On Tue, Aug 21, 2007 at 09:11:56PM +0545, kanishk rastogi wrote:
> I was looking at the xfs_write code path in kernel 2.6.20 .......
> I saw it acquiring inode->i_mutex .
> Whats the need ?
> What are we safegaurding inode for.

See Documentation/filesystems/Locking and other files in that
directory for what i_mutex is supposed to protect.

XFS is different as it has it's own inodes and inode locks, but
it still mostly uses i_mutex inteh accepted way.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group

Re: Need of inode->i_mutex in xfs_write()

[kanishk rastogi]

On 8/24/07, David Chinner <dgc@sgi.com> wrote:
> On Tue, Aug 21, 2007 at 09:11:56PM +0545, kanishk rastogi wrote:
> > I was looking at the xfs_write code path in kernel 2.6.20 .......
> > I saw it acquiring inode->i_mutex .
> > Whats the need ?
> > What are we safegaurding inode for.
>
> See Documentation/filesystems/Locking and other files in that
> directory for what i_mutex is supposed to protect.
>
> XFS is different as it has it's own inodes and inode locks, but
> it still mostly uses i_mutex inteh accepted way.
>

xfs_write comes in file_operations->aio_write()
and the documentation doesnt say anything for it to acquire i_mutex in
that path.

I still fail to understand its usage.

Where i am going wrong.

regards
kanishk






> Cheers,
>
> Dave.
> --
> Dave Chinner
> Principal Engineer
> SGI Australian Software Group
>

Re: Need of inode->i_mutex in xfs_write()

[David Chinner]

On Fri, Sep 07, 2007 at 11:28:27AM +0545, kanishk rastogi wrote:
> On 8/24/07, David Chinner <dgc@sgi.com> wrote:
> > On Tue, Aug 21, 2007 at 09:11:56PM +0545, kanishk rastogi wrote:
> > > I was looking at the xfs_write code path in kernel 2.6.20 .......
> > > I saw it acquiring inode->i_mutex .
> > > Whats the need ?
> > > What are we safegaurding inode for.
> >
> > See Documentation/filesystems/Locking and other files in that
> > directory for what i_mutex is supposed to protect.
> >
> > XFS is different as it has it's own inodes and inode locks, but
> > it still mostly uses i_mutex inteh accepted way.
> >
> 
> xfs_write comes in file_operations->aio_write()
> and the documentation doesnt say anything for it to acquire i_mutex in
> that path.

The i_mutex is supposed to be held across various calls into
generic code. See generic_file_aio_write() for the common
implementation of ->aio_write(). The entire write path is
supposed to be protected by the i_mutex.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group