freebsd stable - Jul 2016 - Reproducable panic in FFS with softupdates and no journaling (10.3-RELEASE-pLATEST)

On Wed, Jul 06, 2016 at 12:02:00PM -0400, David Cross
wrote:
> Oh, whoops; how do I printout the buffer?
In kgdb, p/x *(struct buf *)address

(kgdb) up 5
#5  0xffffffff804aafa1 in brelse (bp=0xfffffe00f77457d0) at buf.h:428
428                     (*bioops.io_deallocate)(bp);
Current language:  auto; currently minimal
(kgdb) p/x *(struct buf *)0xfffffe00f77457d0
$1 = {b_bufobj = 0xfffff80002e88480, b_bcount = 0x4000, b_caller1 = 0x0,
  b_data = 0xfffffe00f857b000, b_error = 0x0, b_iocmd = 0x0, b_ioflags 0x0,
  b_iooffset = 0x0, b_resid = 0x0, b_iodone = 0x0, b_blkno = 0x115d6400,
  b_offset = 0x0, b_bobufs = {tqe_next = 0x0, tqe_prev 0xfffff80002e884d0},
  b_vflags = 0x0, b_freelist = {tqe_next = 0xfffffe00f7745a28,
    tqe_prev = 0xffffffff80c2afc0}, b_qindex = 0x0, b_flags = 0x20402800,
  b_xflags = 0x2, b_lock = {lock_object = {lo_name = 0xffffffff8075030b,
      lo_flags = 0x6730000, lo_data = 0x0, lo_witness 0xfffffe0000602f00},
    lk_lock = 0xfffff800022e8000, lk_exslpfail = 0x0, lk_timo = 0x0,
    lk_pri = 0x60}, b_bufsize = 0x4000, b_runningbufspace = 0x0,
  b_kvabase = 0xfffffe00f857b000, b_kvaalloc = 0x0, b_kvasize = 0x4000,
  b_lblkno = 0x0, b_vp = 0xfffff80002e883b0, b_dirtyoff = 0x0,
  b_dirtyend = 0x0, b_rcred = 0x0, b_wcred = 0x0, b_saveaddr = 0x0, b_pager
= {
    pg_reqpage = 0x0}, b_cluster = {cluster_head = {tqh_first = 0x0,
      tqh_last = 0x0}, cluster_entry = {tqe_next = 0x0, tqe_prev = 0x0}},
  b_pages = {0xfffff800b99b30b0, 0xfffff800b99b3118, 0xfffff800b99b3180,
    0xfffff800b99b31e8, 0x0 <repeats 28 times>}, b_npages = 0x4, b_dep = {
    lh_first = 0xfffff800023d8c00}, b_fsprivate1 = 0x0, b_fsprivate2 = 0x0,
  b_fsprivate3 = 0x0, b_pin_count = 0x0}


This is the freshly allocated buf that causes the panic; is this what is
needed?  I "know" which vnode will cause the panic on vnlru cleanup,
but I
don't know how to walk the memory list without a 'hook'.. as in, i
can
setup the kernel in a state that I know will panic when the vnode is
cleaned up, I can force a panic 'early' (kill -9 1), and then I could
get
that vnode.. if I could get the vnode list to walk.

On Wed, Jul 6, 2016 at 1:37 PM, Konstantin Belousov <kostikbel at
gmail.com>
wrote:
> On Wed, Jul 06, 2016 at 12:02:00PM -0400, David Cross wrote:
> > Oh, whoops; how do I printout the buffer?
>
> In kgdb, p/x *(struct buf *)address
>