linux-kernel - Re: [RFC PATCH] ceph: fix cross quota realms renames with new truncated files

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Date:   Wed, 11 Nov 2020 18:28:02 +0000
From:   Luis Henriques <lhenriques@...e.de>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ceph: fix cross quota realms renames with new
 truncated files

Jeff Layton <jlayton@...nel.org> writes:

> On Wed, 2020-11-11 at 15:39 +0000, Luis Henriques wrote:
>> When doing a rename across quota realms, there's a corner case that isn't
>> handled correctly.  Here's a testcase:
>> 
>>   mkdir files limit
>>   truncate files/file -s 10G
>>   setfattr limit -n ceph.quota.max_bytes -v 1000000
>>   mv files limit/
>> 
>> The above will succeed because ftruncate(2) won't result in an immediate
>> notification of the MDSs with the new file size, and thus the quota realms
>> stats won't be updated.
>> 
>> This patch forces a sync with the MDS every time there's an ATTR_SIZE that
>> sets a new i_size, even if we have Fx caps.
>> 
>> Cc: stable@...r.kernel.org
>> Fixes: dffdcd71458e ("ceph: allow rename operation under different quota realms")
>> URL: https://tracker.ceph.com/issues/36593
>> Signed-off-by: Luis Henriques <lhenriques@...e.de>
>> ---
>>  fs/ceph/inode.c | 11 ++---------
>>  1 file changed, 2 insertions(+), 9 deletions(-)
>> 
>> diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
>> index 526faf4778ce..30e3f240ac96 100644
>> --- a/fs/ceph/inode.c
>> +++ b/fs/ceph/inode.c
>> @@ -2136,15 +2136,8 @@ int __ceph_setattr(struct inode *inode, struct iattr *attr)
>>  	if (ia_valid & ATTR_SIZE) {
>>  		dout("setattr %p size %lld -> %lld\n", inode,
>>  		     inode->i_size, attr->ia_size);
>> -		if ((issued & CEPH_CAP_FILE_EXCL) &&
>> -		    attr->ia_size > inode->i_size) {
>> -			i_size_write(inode, attr->ia_size);
>> -			inode->i_blocks = calc_inode_blocks(attr->ia_size);
>> -			ci->i_reported_size = attr->ia_size;
>> -			dirtied |= CEPH_CAP_FILE_EXCL;
>> -			ia_valid |= ATTR_MTIME;
>> -		} else if ((issued & CEPH_CAP_FILE_SHARED) == 0 ||
>> -			   attr->ia_size != inode->i_size) {
>> +		if ((issued & (CEPH_CAP_FILE_EXCL|CEPH_CAP_FILE_SHARED)) ||
>> +		    (attr->ia_size != inode->i_size)) {
>>  			req->r_args.setattr.size = cpu_to_le64(attr->ia_size);
>>  			req->r_args.setattr.old_size =
>>  				cpu_to_le64(inode->i_size);
>
> Hmm...this makes truncates more expensive when we have caps. I'd rather
> not do that if we can help it.

Yeah, as I mentioned in the tracker, there's indeed a performance impact
with this fix.  That's what made me add the RFC in the subject ;-)

> What about instead having the client mimic a fsync when there is a
> rename across quota realms? If we can't tell that reliably then we could
> also just do an effective fsync ahead of any cross-directory rename?

Ok, thanks for the suggestion.  That may actually work, although it will
make the rename more expensive of course.  I'll test that tomorrow and
eventually follow-up with a patch.

Cheers,
-- 
Luis