[Bug 210800] hung process using ktrace with cloudabi

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=210800

            Bug ID: 210800
           Summary: hung process using ktrace with cloudabi
           Product: Base System
           Version: 11.0-CURRENT
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: mfp49_freebsd at plass-family.net
                CC: freebsd-amd64 at FreeBSD.org
                CC: freebsd-amd64 at FreeBSD.org

Using ktrace on a cloudabi executable sometimes hangs in such a way that it
cannot be killed.

FreeBSD xx 11.0-ALPHA5 FreeBSD 11.0-ALPHA5 #0 r302164: Fri Jun 24 02:51:52 UTC
2016     root at releng2.nyi.freebsd.org:/usr/obj/usr/src/sys/GENERIC  amd64

# kldload cloudabi
# kldload cloudabi64

$ pkg info | grep cloud
cloudabi-0.6                   Constants, types and data structures used by
CloudABI
cloudabi-toolchain-1.4         C and C++ toolchain for CloudABI
cloudabi-utils-0.11            Utilities for running CloudABI programs
x86_64-unknown-cloudabi-cloudabi-0.6_1 cloudabi for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-cloudlibc-0.40_1 cloudlibc for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-compiler-rt-3.8.0_4 compiler-rt for
x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-curl-7.49.1_2 curl for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-cxx-runtime-1.0_2 cxx-runtime for
x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-libcxx-3.8.0_9 libcxx for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-libcxxabi-3.8.0_6 libcxxabi for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-libressl-2.4.1_1 libressl for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-libunwind-3.8.0_5 libunwind for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-lua-5.3.3_2 lua for x86_64-unknown-cloudabi
x86_64-unknown-cloudabi-zlib-1.2.8_11 zlib for x86_64-unknown-cloudabi

$ : | ktrace /usr/local/x86_64-unknown-cloudabi/bin/lua

Here is a kernel stack trace of the hung process:
(kgdb) where
#0  sched_switch (td=0xfffff8006a217000, newtd=0xfffff80007380a00, 
    flags=<value optimized out>) at /usr/src/sys/kern/sched_ule.c:1973
#1  0xffffffff80a52a87 in mi_switch (flags=260, newtd=0x0)
    at /usr/src/sys/kern/kern_synch.c:455
#2  0xffffffff80a95d27 in sleepq_switch (wchan=<value optimized out>, pri=0)
    at /usr/src/sys/kern/subr_sleepqueue.c:557
#3  0xffffffff80a95bf3 in sleepq_wait (wchan=0xffffffff81c34400, pri=0)
    at /usr/src/sys/kern/subr_sleepqueue.c:637
#4  0xffffffff809e8cc4 in _cv_wait (cvp=<value optimized out>, 
    lock=<value optimized out>) at /usr/src/sys/kern/kern_condvar.c:144
#5  0xffffffff80aa3132 in vmem_xalloc (vm=<value optimized out>, 
    size0=<value optimized out>, align=<value optimized out>, phase=0, 
    nocross=<value optimized out>, minaddr=0, maxaddr=<value optimized out>, 
    flags=8194, addrp=<value optimized out>)
    at /usr/src/sys/kern/subr_vmem.c:1209
#6  0xffffffff80aa2e72 in vmem_alloc (vm=0xffffffff81c34380, size=14244610048, 
    flags=8194, addrp=0xfffffe01212959f0) at /usr/src/sys/kern/subr_vmem.c:1095
#7  0xffffffff80d2c193 in kmem_malloc (vmem=0xffffffff81c34380, 
    size=14244610048, flags=2) at /usr/src/sys/vm/vm_kern.c:313
#8  0xffffffff80d24d46 in uma_large_malloc (size=14244610048, wait=2)
    at /usr/src/sys/vm/uma_core.c:1106
#9  0xffffffff80a25833 in malloc (size=<value optimized out>, 
    mtp=0xffffffff818f0780, flags=2) at /usr/src/sys/kern/kern_malloc.c:510
#10 0xffffffff80a189ad in ktrsyscall (code=35, narg=1780576256, 
    args=0xfffffe0121295b80) at /usr/src/sys/kern/kern_ktrace.c:451
#11 0xffffffff80eb893e in amd64_syscall (td=0xfffff8006a217000, traced=0)
    at subr_syscall.c:77
#12 0xffffffff80e9897b in Xfast_syscall ()
    at /usr/src/sys/amd64/amd64/exception.S:396
#13 0x000000000103f42b in ?? ()

Clearly narg is ktrsyscall is garbage. It looks like
cloudabi64_fetch_syscall_args() is not filling in sa->nargs.

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