Re: [PATCH] cifs: WARN_ON_ONCE if kernel_sendmsg() returns -ENOSPC

[Suresh Jayaraman <sjayaraman-IBi9RG/b67k@public.gmane.org>]

On 10/03/2012 03:34 PM, Jeff Layton wrote:
> On Wed, 03 Oct 2012 12:45:36 +0530
> Suresh Jayaraman <sjayaraman-IBi9RG/b67k@public.gmane.org> wrote:
> 
>> kernel_sendmsg() is less likely to return -ENOSPC and it might be
>> a bug to do so. However, in the past there might have been cases
>> where a -ENOSPC was returned from a low level driver.
>>
>> Add a WARN_ON_ONCE() to ensure that it is safe to assume that -ENOSPC
>> is no longer returned. This -ENOSPC specific handling will be removed
>> once we are sure it is no longer returned.
>>
>> Also, avoid setting -ENOSPC to -EAGAIN while at it.
>>
>> Cc: Jeff Layton <jlayton-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>> Signed-off-by: Suresh Jayaraman <sjayaraman-IBi9RG/b67k@public.gmane.org>
>> ---
>>  fs/cifs/transport.c |    5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
>> index d9b639b..afe000f 100644
>> --- a/fs/cifs/transport.c
>> +++ b/fs/cifs/transport.c
>> @@ -155,6 +155,10 @@ smb_sendv(struct TCP_Server_Info *server, struct kvec *iov, int n_vec)
>>  		rc = kernel_sendmsg(ssocket, &smb_msg, &iov[first_vec],
>>  				    n_vec - first_vec, total_len);
>>  		if ((rc == -ENOSPC) || (rc == -EAGAIN)) {
>> +			/*
>> +			 * Catch if a low level driver returns -ENOSPC.
>> +			 */
>> +			WARN_ON_ONCE(rc == -ENOSPC);
>>  			i++;
>>  			/*
>>  			 * If blocking send we try 3 times, since each can block
>> @@ -177,7 +181,6 @@ smb_sendv(struct TCP_Server_Info *server, struct kvec *iov, int n_vec)
>>  			if ((i >= 14) || (!server->noblocksnd && (i > 2))) {
>>  				cERROR(1, "sends on sock %p stuck for 15 seconds",
>>  				    ssocket);
>> -				rc = -EAGAIN;
> 
> Do you really want to remove this reset? This will change the behavior
> if the lower levels do indeed return -ENOSPC. That will now bubble back
> up to the upper levels and it will likely abort the call instead of
> retrying.

Yes, you are correct. I'll remove it.

> 
> I think it would be best that we add the WARN_ON_ONCE but not change
> anything else. If no one reports seeing that warning fire for 2 or 3
> releases then we can safely remove the -ENOSPC handling. Maybe shoot
> for that in 3.10 or so?
> 
> You may want to add a comment to remind us to revisit that for the 3.10
> cycle.
> 

Sure, I'll add that when I respin.


Thanks
Suresh