Re: kern/42455: tstile hang with nfs

["Christoph Egger" <Christoph_Egger%gmx.de@localhost>]

>  >  
>  >  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.
>  
>  nfs_subs.c:968 is the line in error:
>  
>             do {
>                      m2 = m_get(M_WAIT, MT_DATA);
>                      MCLAIM(m2, m1->m_owner);
>                      if (left >= MINCLSIZE) {
>                              MCLGET(m2, M_WAIT);
>                      }
>                      m2->m_next = *nextp; <-- BUG happens here!!
>                      *nextp = m2;
>                      nextp = &m2->m_next;
>  

This is the code path from entering nfsm_disct() till when
the bug happens:

897:    m1 = *mdp;
903:    while (left == 0) {
921:    if ((m1->m_flags & M_EXT) != 0) {
922:            if (havebuf && M_TRAILINGSPACE(havebuf) >= siz &&
923:                nfsm_aligned(mtod(havebuf, char *) + havebuf->m_len)) {
959:                    struct mbuf **nextp = &m1->m_next;
961:                    m1->m_len -= left;
962:                    do {
963:                            m2 = m_get(M_WAIT, MT_DATA);
964:                            MCLAIM(m2, m1->m_owner);
965:                            if (left >= MINCLSIZE) {
968:                            m2->m_next = *nextp;


Christoph