Re: writeable file with no mnt_want_write()

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Jul 03, 2008 at 03:21:58PM +0300, Benny Halevy wrote:
> Bruce,
> 
> I'm seeing this warning on the open_downgrade path
> when running the newpynfs tests:
> 
> Jul  3 07:32:50 buml kernel: writeable file with no mnt_want_write()
> Jul  3 07:32:50 buml kernel: ------------[ cut here ]------------
> Jul  3 07:32:50 buml kernel: WARNING: at /usr0/export/dev/bhalevy/git/linux-pnfs-bh-nfs41/include/linux/fs.h:855 drop_file_write_access+0x6b/0x7e()
> Jul  3 07:32:50 buml kernel: Modules linked in: nfsd auth_rpcgss exportfs nfs lockd nfs_acl sunrpc
> Jul  3 07:32:50 buml kernel: Call Trace: 
> Jul  3 07:32:50 buml kernel: 6eaadc88:  [<6002f471>] warn_on_slowpath+0x54/0x8e
> Jul  3 07:32:50 buml kernel: 6eaadcc8:  [<601b790d>] printk+0xa0/0x793
> Jul  3 07:32:50 buml kernel: 6eaadd38:  [<601b6205>] __mutex_lock_slowpath+0x1db/0x1ea
> Jul  3 07:32:50 buml kernel: 6eaadd68:  [<7107d4d5>] nfs4_preprocess_seqid_op+0x2a6/0x31c [nfsd]
> Jul  3 07:32:50 buml kernel: 6eaadda8:  [<60078dc9>] drop_file_write_access+0x6b/0x7e
> Jul  3 07:32:50 buml kernel: 6eaaddc8:  [<710804e4>] nfsd4_open_downgrade+0x114/0x1de [nfsd]
> Jul  3 07:32:50 buml kernel: 6eaade08:  [<71076215>] nfsd4_proc_compound+0x1ba/0x2dc [nfsd]
> Jul  3 07:32:50 buml kernel: 6eaade48:  [<71068221>] nfsd_dispatch+0xe5/0x1c2 [nfsd]
> Jul  3 07:32:50 buml kernel: 6eaade88:  [<71312f81>] svc_process+0x3fd/0x714 [sunrpc]
> Jul  3 07:32:50 buml kernel: 6eaadea8:  [<60039a81>] kernel_sigprocmask+0xf3/0x100
> Jul  3 07:32:50 buml kernel: 6eaadee8:  [<7106874b>] nfsd+0x182/0x29b [nfsd]
> Jul  3 07:32:50 buml kernel: 6eaadf48:  [<60021cc9>] run_kernel_thread+0x41/0x4a
> Jul  3 07:32:50 buml kernel: 6eaadf58:  [<710685c9>] nfsd+0x0/0x29b [nfsd]
> Jul  3 07:32:50 buml kernel: 6eaadf98:  [<60021cb0>] run_kernel_thread+0x28/0x4a
> Jul  3 07:32:50 buml kernel: 6eaadfc8:  [<60013829>] new_thread_handler+0x72/0x9c
> Jul  3 07:32:50 buml kernel: 
> Jul  3 07:32:50 buml kernel: ---[ end trace 2426dd7cb2fba3bf ]---
> 
> I'm not sure what would be the right fix for that...

Yes.  I'm a bit confused about that.  Hm, maybe we need to be doing a
mnt_want_write on open_upgrade and mnt_put_write on downgrade?

> The following could be unrelated, and maybe I'm just confused
> but there seems to be something funky about the way we convert
> from bmap to access bits.
> (unrelated note: for nfsv4.1 we'll need to mask the share access with
> ~OPEN4_SHARE_ACCESS_WANT_DELEG_MASK)
> 
> If I understand this correctly, we set a bit in 
> st_access_bmap corresponding to the share_access,
> so for read-only bit #1 will be, write-only #2,
> and for read-write (only) bits 1-3 should be set.

No, in that case only the third bit 3 should be set.

We're just trying to enforce rfc 3530 14.2.19:

	"The share_access and share_deny bits specified must be exactly
	equal to the union of the share_access and share_deny bits
	specified for some subset of the OPENs in effect for current
	openowner on the current file.  If that constraint is not
	respected, the error NFS4ERR_INVAL should be returned."

Note that this paragraph would allow

	OPEN for read
	OPEN for write
	OPEN_DOWNGRADE to read


but have us return NFS4ERR_INVAL if we got a sequence of opens like:

	OPEN for read and write
	OPEN_DOWNGRADE to read

because in this case there was only a single open (for read and write),
and no open just for read.

--b.

> otherwise this wouldn't work:
> 	if (!test_bit(od->od_share_access, &stp->st_access_bmap)) {
> 		dprintk("NFSD:access not a subset current bitmap: 0x%lx, input access=%08x\n",
> 			stp->st_access_bmap, od->od_share_access);
> 		goto out;
> 	}
> 
> but init_stateid sets only one bit:
> 	__set_bit(open->op_share_access, &stp->st_access_bmap);
> 
> only if we went through nfs4_upgrade_open another bit may be set.
> 
> Benny