Re: mysterious setting of B_DIRECT?

On Thu, Apr 25, 2024 at 07:49:23PM -0700, Rick Macklem wrote:
> Hi,
> 
> This week I have been doing active testing as a part of an IETF
> bakeathon for NFSv4. During the week I had a NFSv4 client
> crash. On the surface, it is straightforward, in that it called
> ncl_doio_directwrite() and the field called b_caller1 was NULL.
> 
> Now, here's the weird part...
> ncl_doio_directwrite() should never be called because B_DIRECT
> should never be set. (The only place B_DIRECT gets set in the code
> is never currently executed.)
Do you mean the place in nfs_directio_write()?  And the fact that
IO_SYNC is always set.

> 
> I have a patch that clears out the "never to be executed" code and
> this seems to avoid the patch, since with the patch, ncl_doio_directwrite()
> no longer exists.
> 
> What I cannot figure out is how B_DIRECT got set?
> I can note that UFS was under heavy load when the client crashed,
> but I cannot see how a UFS "struct buf" would become a NFS "struct buf"
> without b_flags being set to 0.

There are also vfs_bio_brelse()/vfs_bio_setflags() functions which can
set B_DIRECT.  On the other hand, they are not used by nfs client.

What was the overall state of the buffer with the B_DIRECT flag?  Which
vnode it was assigned to?