Kernel panic caused by diagnostic assertion in PHP

[JelteF]

I'm getting a kernel panic after putting some load on my PHP kernel for a while. Can you give me some helpin debugging this issue?

=== calling "../bin/php-cgi.bin" main() ===

rumprun: call to ``_sys___sigprocmask14'' ignored
rumprun: call to ``sigaction'' ignored
panic: kernel diagnostic assertion "ph == NULL || ((pp->pr_roflags & PR_PHINPAGE) != 0) || ((char *)ph->ph_page <= (char *)v && (char *)v < (char *)ph->ph_page + pp->pr_alloc->pa_pagesz)" failed: file "/root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../
rump kernel halting...
PANIC: rumpuser panic
port 4 still bound!
port 5 still bound!
minios: halting, reason=0

[anttikantee]

Smells like memory corruption.

But for starters, can you post the backtrace? Instructions are here: http://wiki.rumpkernel.org/Howto%3A-Debugging-Rumprun-with-gdb

[Incognito]

Are you running PHP as a standalone server? I'm curious if this issue is in PHP.

[JelteF]

I'm runnig PHP behind Nginx and it connects to MySQL using mysql_pconnect

[JelteF]

@anttikantee When I try the instructions there I get:

+ rumprun xen -D 2222 -di -M 128 -I net1,xenif -W net1,inet,static,145.100.105.229/24 -b ../images/data.iso,/data -e PHP_FCGI_MAX_REQUESTS=0 -- ../bin/php-cgi.bin -b 8000

!!!
!!! NOTE: rumprun is experimental. syntax may change in the future
!!!

/root/rumprun/rumprun/bin/rumprun: 508: /root/rumprun/rumprun/bin/rumprun: gdbsx: parameter not set

Any clue on how to fix that?

[anttikantee]

@JelteF yes, see https://github.com/rumpkernel/rumprun/blob/master/app-tools/rumprun#L435-L442

So essentially you must teach the script where to find gdbsx from. If you want to submit a patch to fix that, maybe it should also be possible for the user to override the search by setting $GDBSX.

btw, in my experience the Xen debugger backend (gdbsx) does not work very well. I'd rather suggest trying to debug the problem under qemu/kvm, if possible -- you may get a better backtrace that way.

[JelteF]

I finally got a backtrace for this:

NU gdb (Ubuntu 7.10-1ubuntu2) 7.10
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Reading symbols from ../bin/php-cgi.bin...done.
Remote debugging using :2012
0x0000000000102669 in hlt () at include/arch/x86/inline.h:59
59              __asm__ __volatile__("hlt");
(gdb) bt
#0  0x0000000000102669 in hlt () at include/arch/x86/inline.h:59
#1  bmk_platform_halt (panicstring=panicstring@entry=0xb02030 "rumpuser panic") at kernel.c:59
#2  0x000000000010cfba in rumpuser_exit (value=value@entry=-1) at /root/rumprun/lib/libbmk_rumpuser/rumpuser_base.c:137
#3  0x0000000000861b27 in cpu_reboot (howto=<optimized out>, bootstr=<optimized out>) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/emul.c:393
#4  0x0000000000829118 in vpanic (fmt=0xb7db08 "kernel %sassertion \"%s\" failed: file \"%s\", line %d ", ap=0x7f17dc8) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_prf.c:342
#5  0x0000000000812f82 in kern_assert (fmt=<optimized out>) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../lib/libkern/kern_assert.c:51
#6  0x000000000082c294 in pr_find_pagehead (v=0x7520000, pp=0xe72240) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:352
#7  pool_do_put (pq=0x7f17e28, v=0x7520000, pp=0xe72240) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:980
#8  pool_put (pp=pp@entry=0xe72240, v=v@entry=0x7520000) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:1077
#9  0x000000000082c95d in pool_cache_destruct_object1 (object=0x7520000, pc=0xe72240) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:1954
#10 pool_cache_invalidate_groups (pc=pc@entry=0xe72240, pcg=pcg@entry=0xe7eb00) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:1989
#11 0x000000000082d76d in pool_cache_invalidate (pc=0xe72240) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:2055
#12 0x000000000082d857 in pool_reclaim (pp=pp@entry=0xe72240) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:1360
#13 0x000000000082db1d in pool_drain (ppp=0x7f17f88) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/../../../kern/subr_pool.c:1445
#14 0x000000000085d614 in uvm_pageout (arg=<optimized out>) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/vm.c:1161
#15 0x000000000085e23e in threadbouncer (arg=0xe7a2d0) at /root/rumprun/src-netbsd/sys/rump/librump/rumpkern/threads.c:90
#16 0x000000000010d7c8 in bmk_cpu_sched_bouncer ()
#17 0x0000000000000000 in ?? ()
(gdb) 

[anttikantee]

Ok, so with kvm (or qemu). In case it's easy to repeat, do you always see uvm_pageout() in the stack trace?

[JelteF]

yes with kvm. I will try to repeat it again (since I'm also trying to get mysql to crash with kvm). I'm guessing the problem is the same though, as it causes the same output as the previous crash.

[JelteF]

I got the crash once more and the backtrace was exactly the same. One interesting thing is that we load balance our tests (using an nginx unikernel) to 5 php unikernels and they all crash at the same moment.

Also we found out that the default memory limit of php is 128M (using phpinfo.php) and the unikernel is assigned 128M in the default script (which we use). So that might be the issue here :).

[JelteF]

Setting the memory -M option to 160 did not fix the crash. We will try tomorrow with 256.

[Incognito]

For the record, in PHP (when running on Linux or something) I've seen "PHP Fatal error: Out of memory" when physical memory is exhausted, and a different error when it's a config thing ("Fatal error: Allowed memory size of 12582912 bytes exhausted (tried to allocate 23456789 bytes.... ")

[anttikantee]

I'd try with something like -M 512. There are various degrees of overhead, so having 256MB of memory does not provide php with 128MB. (some of them could me optimized, but requires finishing the work which allows memory to be shared between the application and system)