Re: [RFC PATCH] NFSD: Remove WARN_ON_ONCE in nfsd_iter_read()

[Chuck Lever <cel@kernel.org>]

On 9/13/25 1:37 AM, NeilBrown wrote:
>> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
>> index 714777c221ed..e2f0fe3f82c0 100644
>> --- a/fs/nfsd/vfs.c
>> +++ b/fs/nfsd/vfs.c
>> @@ -1120,13 +1120,13 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
>>  		bvec_set_page(&rqstp->rq_bvec[v], *(rqstp->rq_next_page++),
>>  			      len, base);
>>  		total -= len;
>> -		++v;
>>  		base = 0;
>> +		if (++v >= rqstp->rq_maxpages)
>> +			break;
> I would have changed the head of the while loop to be
> 
>   while (total > 0 && rqstp->rq_next_page < ....)
> 
> and then realised that I don't know what to put there.
> I don't think that counting up to rq_maxpages is safe when there could
> be two READ ops in an NFSv4 Compound.
> 
> And if we are cleaning up this function I woul put the increments of v
> and rq_next_page next to each other..
> </bikeshed>
> 
> The patch is an improvement.  I wonder if it is enough.

I'm planning a second patch that adds protection against overrunning
the rq_pages array. Is there anything else you feel is needed?


-- 
Chuck Lever