Re: [PATCH] mm: fix possible cause of a page_mapped BUG

From: Robert ÅwiÄcki
Date: Tue Apr 12 2011 - 12:19:20 EST

>>> So, if this case is not caught later on in the code, I guess it solves
>>> the problem. During the fuzzing I didn't experience any panic's, but
>>> some other problems arose, i.e. cannot read /proc/<pid>/maps for some
>>> processes (sys_read hangs, and such process cannot be killed or
>>> stopped with any signal, still it's running (R state) and using CPU -
>>> I'll submit another report for that).
>> Hmm. Sounds like an endless loop in kernel mode.
>> Use "perf record -ag" as root, it should show up very clearly in the report.
>> Â Â Â Â Â Â Â Â Â Â Â Â ÂLinus
> I've put some data here -
> - I think it's somewhat connected (sys_mlock appears on both cases).
> Attaching perf data (for 2.6.38) + kdb dumpall + procdump for process 14158
> Those 3 processes cannot be stopped/killed
> 14158 66.2 Â0.0 Â 8380 Â3012 ? ÂRL Â/tmp/iknowthis
> 17100 63.6 Â0.1 Â18248 Â4004 ? ÂRL Â/tmp/iknowthis
> 19772 63.8 Â0.0 Â 4000 Â1888 ? Â RL Â/tmp/iknowthis

Also, the system doesn't look usable after such fuzzing (executing a
few times some pretty deterministic program)

root@ise-test:~# gcc -m32 mlock.c -o mlock

root@ise-test:~# ./mlock
./mlock: relocation error: ./mlock: symbol perror, version GLIBC_2.0
not defined in file with link time reference

root@ise-test:~# ./mlock
mmap: Success
RET: 0xf751f000
mremap: Invalid argument
RET: 0xffffffff

root@ise-test:~# ./mlock
Segmentation fault

root@ise-test:~# dmesg | tail -n 1
[ 5164.961568] mlock[7097]: segfault at 0 ip (null) sp
00000000ff8a00d4 error 14 in mlock[8048000+1000]

Robert ÅwiÄcki
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