Re: [PATCH] nfsd: take file and mnt write in nfs4_upgrade_open

[Benny Halevy <bhalevy@panasas.com>]

On Jul. 07, 2008, 22:25 +0300, "J. Bruce Fields" <bfields@fieldses.org> wrote:
> Yes, this looks correct, at least for the immediate fix; thanks!
> 
> Eventually I think we should move to opening a new file descriptor when
> upgrading, and keeping two file descriptors with the stateid; I think
> this business of trying to use a file descriptor for write when we
> opened it for read is probably wrong.

That could work, though they need to be associated in some way
for open_downgrade/close processing.

Benny

> 
> --b.
> 
> On Fri, Jul 04, 2008 at 03:38:41PM +0300, Benny Halevy wrote:
>> testing with newpynfs revealed this warning:
>> 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 ]---
>>
>> Bruce Fields suggested this (Thanks!):
>> maybe we need to be doing a mnt_want_write on open_upgrade and mnt_put_write on downgrade?
>>
>> This patch adds a call to mnt_want_write and file_take_write (which is
>> doing the actual work).
>>
>> The counter-calls mnt_drop_write a file_release_write are now being properly
>> called by drop_file_write_access in the exact path printed by the warning
>> above.
>>
>> Signed-off-by: Benny Halevy <bhalevy@panasas.com>
>> ---
>>  fs/nfsd/nfs4state.c |    4 ++++
>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
>> index 0d1760f..4263445 100644
>> --- a/fs/nfsd/nfs4state.c
>> +++ b/fs/nfsd/nfs4state.c
>> @@ -1570,6 +1570,10 @@ nfs4_upgrade_open(struct svc_rqst *rqstp, struct svc_fh *cur_fh, struct nfs4_sta
>>  		int err = get_write_access(inode);
>>  		if (err)
>>  			return nfserrno(err);
>> +		err = mnt_want_write(cur_fh->fh_export->ex_path.mnt);
>> +		if (err)
>> +			return nfserrno(err);
>> +		file_take_write(filp);
>>  	}
>>  	status = nfsd4_truncate(rqstp, cur_fh, open);
>>  	if (status) {
>> -- 
>> 1.5.6.GIT
>>