Re: [PATCH v2] NFS: don't raise i_size for DEALLOCATE in _nfs42_proc_fallocate()

["Anna Schumaker" <anna@kernel.org>]

Hi Joseph,

On Thu, Nov 12, 2026, at 8:02 PM, Joseph Qi wrote:
> Ping...

I have this patch applied to a private branch for my own testing and it
seems okay to me so far. I'm planning to test with it for a bit before
sending it in to a v7.4-rc.

Anna

>
> On 11/9/26 7:32 PM, Joseph Qi wrote:
>> _nfs42_proc_fallocate() raises i_size to offset + len on success, so
>> that the cached size is not left stale when a delegation blocks the
>> post-op attribute refresh.  The helper is shared by all three
>> fallocate modes, but DEALLOCATE always carries FALLOC_FL_KEEP_SIZE
>> and never extends the file on the server, so punching a hole that
>> reaches past EOF now wrongly enlarges the cached i_size.
>> 
>> The post-op update would normally restore the size from the returned
>> attributes, but nfs_update_inode() applies a differing size only when
>> no delegation is held, and then only when no write is in flight or the
>> new size is larger:
>> 
>> 	if (new_isize != cur_isize && !have_delegation) {
>> 		if (!nfs_have_writebacks(inode) || new_isize > cur_isize)
>> 			i_size_write(inode, new_isize);
>> 	}
>> 
>> With a concurrent mmap writer (nrequests != 0) or any outstanding
>> delegation, the shrinking server size is therefore ignored and the
>> client keeps reporting a file larger than the server has, in violation
>> of KEEP_SIZE, until some later revalidation without writebacks happens
>> to fix it up.
>> 
>> Skip the i_size bump for the DEALLOCATE procedure.  ALLOCATE (mode 0)
>> and ZERO_RANGE (which nfs42_fallocate() accepts only without
>> FALLOC_FL_KEEP_SIZE) do extend the file when the range reaches past
>> EOF, so they keep the update.
>> 
>> Fixes: 35168eb947f2 ("NFS: fix eof updates after NFSv4.2 fallocate/zero-range")
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
>> ---
>>  fs/nfs/nfs42proc.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>> 
>> diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
>> index ab86246fc364f..d76bface87f74 100644
>> --- a/fs/nfs/nfs42proc.c
>> +++ b/fs/nfs/nfs42proc.c
>> @@ -84,7 +84,9 @@ static int _nfs42_proc_fallocate(struct rpc_message *msg, struct file *filep,
>>  		loff_t newsize = offset + len;
>>  
>>  		spin_lock(&inode->i_lock);
>> -		if (newsize > i_size_read(inode))
>> +		/* DEALLOCATE implies KEEP_SIZE, so don't extend i_size */
>> +		if (msg->rpc_proc != &nfs4_procedures[NFSPROC4_CLNT_DEALLOCATE] &&
>> +		    newsize > i_size_read(inode))
>>  			i_size_write(inode, newsize);
>>  		nfs_set_cache_invalid(inode, NFS_INO_INVALID_BLOCKS);
>>  		if (nfs_should_remove_suid(inode))