Re: kern/42455: tstile hang with nfs

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

The following reply was made to PR kern/42455; it has been noted by GNATS.

From: yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)
To: Christoph_Egger%gmx.de@localhost
Cc: gnats-bugs%NetBSD.org@localhost, netbsd-bugs%netbsd.org@localhost, 
gnats-admin%netbsd.org@localhost,
        kern-bug-people%netbsd.org@localhost
Subject: Re: kern/42455: tstile hang with nfs
Date: Thu, 28 Oct 2010 04:48:41 +0000 (UTC)

 hi,
 
 >>  hi,
 >>  
 >>  >>  >  I added some more debug lines and figured out that the macro
 >>  >>  >  nfsm_wcc_data() drops the mbuf chain w/o decreasing
 >>  >>  >  ctxt.nwc_mbufcount.
 >>  >>  
 >>  >>  The nfsm_wcc_data() macro calls the nfsm_postop_attr() macro.
 >>  >>  The nfsm_postop_attr() macro calls nfsm_loadattrcache() function.
 >>  >>  The nfsm_loadattrcache() function calls nfsm_disct() function.
 >>  >>  
 >>  >>  nfsm_disct() is the function in error which drops the mbuf chain.
 >>  
 >>  are you sure?
 > 
 > yes, absolutely and reproducable.
 > 
 >>  iirc, nwc_mbufcount is about sending mbuf.  otoh, nfsm_disct
 >>  is for received mbuf.
 > 
 > nfs_writerpc *does* call nfsm_disct() through nfsm_wcc_data,
 > nfsm_postop_attr and nfsm_loadattrcache in this order.
 > 
 > So you are saying this should never happen?
 
 i'm saying i don't understand.
 
 nfs_writerpc sends a request to the server, using mreq and mb.
 it's what nwc_mbufcount is used for.
 
 it then parses the reply from the server, using mrep and md.
 it's what nfsm_wcc_data/nfsm_postop_attr/nfsm_loadattrcache/nfsm_disct are
 used for.
 
 i don't understand how a problem in the latter causes the nwc_mbufcount
 problem.  the above two are somehow mixed up?
 
 YAMAMOTO Takashi
 
 > 
 > Christoph