Re: [PATCH] NFSv4: clear exception state on successful mkdir retry

[Thorsten Leemhuis]

On 5/13/26 09:18, Thorsten Leemhuis wrote:
> [top-posting to facilitate processing]
> 
> @NFSv4 maintainers, just wondering, did this patch maybe fall through
> the cracks? It fixes a regression, that's why it's on my radar. Or was
> there some progress and I missed it?

Still no progress afaics. Feels like I'm missing something obvious or
like I'm totally of track.

Igor, Neil, is that the case? Or are you also waiting for the fix to
make progress?

Ciao, Thorsten

> On 4/29/26 12:49, Igor Raits wrote:
>> After a server returns NFS4ERR_DELAY for an NFSv4 CREATE issued by
>> mkdir(2), the client correctly waits and retries.  When the retry
>> succeeds, however, mkdir(2) can still surface -EEXIST to userspace
>> even though the directory was just created on the server.
>>
>> Reproducer (random 16-hex names so collisions are not the cause)
>> against an in-kernel Linux nfsd; reproduces under both NFSv4.0 and
>> NFSv4.2:
>>
>>   N=2000000; base=/var/gdc/export
>>   for ((i=1; i<=N; i++)); do
>>       d=$base/$(openssl rand -hex 8)
>>       mkdir "$d" 2>/dev/null || echo "$(date +%T) failed loop=$i $d"
>>       rmdir "$d" 2>/dev/null
>>   done
>>
>> Failures cluster at the cadence at which the server-side auth/export
>> cache refresh path causes nfsd to return NFS4ERR_DELAY for CREATE.
>>
>> A wire trace of one failure (the three CREATE RPCs all come from a
>> single mkdir(2), generated by the do-while in nfs4_proc_mkdir()):
>>
>>   client -> server  CREATE name=...  -> NFS4ERR_DELAY
>>   ~100 ms later
>>   client -> server  CREATE name=...  -> NFS4_OK         (dir created)
>>   ~80 us later
>>   client -> server  CREATE name=...  -> NFS4ERR_EXIST   (correct)
>>
>> Since commit dd862da61e91 ("nfs: fix incorrect handling of large-number
>> NFS errors in nfs4_do_mkdir()"), nfs4_handle_exception() is called only
>> when _nfs4_proc_mkdir() returned an error.  That gate breaks retry-state
>> hygiene: nfs4_do_handle_exception() resets exception.{delay,recovering,
>> retry} to 0 on entry, so calling it on success is what previously
>> cleared the retry flag set by the preceding NFS4ERR_DELAY iteration.
>> With the gate in place, exception.retry stays at 1 after the successful
>> retry, the loop runs once more, and the resulting CREATE for an
>> already-created name yields NFS4ERR_EXIST -> -EEXIST to userspace.
>>
>> Drop the conditional and call nfs4_handle_exception() unconditionally,
>> matching every other do-while in fs/nfs/nfs4proc.c (nfs4_proc_symlink(),
>> nfs4_proc_link(), etc.).  The dentry/status separation introduced by
>> that commit is preserved.
>>
>> Fixes: dd862da61e91 ("nfs: fix incorrect handling of large-number NFS errors in nfs4_do_mkdir()")
>> Reported-and-tested-by: Jan Čípa <jan.cipa@xxxxxxxxxxxx>
>> Closes: https://lore.kernel.org/linux-nfs/CA+9S74hSp_tJu2Ffe2BPNC2T25gfkhgjjDkdgSsF5c2rnJq_wA@xxxxxxxxxxxxxx/
>> Reviewed-by: NeilBrown <neil@xxxxxxxxxx>
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Igor Raits <igor.raits@xxxxxxxxx>
>> ---
>>  fs/nfs/nfs4proc.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
>> index a0885ae55abc..ffd14141ea1d 100644
>> --- a/fs/nfs/nfs4proc.c
>> +++ b/fs/nfs/nfs4proc.c
>> @@ -5393,10 +5393,9 @@ static struct dentry *nfs4_proc_mkdir(struct inode *dir, struct dentry *dentry,
>>  	do {
>>  		alias = _nfs4_proc_mkdir(dir, dentry, sattr, label, &err);
>>  		trace_nfs4_mkdir(dir, &dentry->d_name, err);
>> +		err = nfs4_handle_exception(NFS_SERVER(dir), err, &exception);
>>  		if (err)
>> -			alias = ERR_PTR(nfs4_handle_exception(NFS_SERVER(dir),
>> -							      err,
>> -							      &exception));
>> +			alias = ERR_PTR(err);
>>  	} while (exception.retry);
>>  	nfs4_label_release_security(label);
>>  
>