Messages in this thread | | | From | Robert Stupp <> | Subject | mlockall(MCL_CURRENT) blocking infinitely | Date | Thu, 24 Oct 2019 09:36:37 +0200 |
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Hi guys,
I've got an issue with `mlockall(MCL_CURRENT)` after upgrading Ubuntu 19.04 to 19.10 - i.e. kernel version change from 5.0.x to 5.3.x.
The following simple program hangs forever with one CPU running at 100% (kernel):
#include <stdio.h> #include <sys/mman.h> int main(char** argv) { printf("Before mlockall(MCL_CURRENT)\n"); // works in 5.0 // hangs forever w/ 5.1 and newer mlockall(MCL_CURRENT); printf("After mlockall(MCL_CURRENT)\n"); }
All kernel versions since 5.1 (tried 5.1.0, 5.1.21, 5.2.21, 5.3.0-19, 5.3.7, 5.4-rc4) show the same symptom (hanging in mlockall(MCL_CURRENT) with 100% kernel-CPU). 5.0 kernel versions (5.0.21) are fine.
First, I thought, that it's something generic, so I tried the above program in a fresh install of Ubuntu eoan (5.3.x) in a VM in virtualbox, but it works fine there. So I suspect, that it has to do with something that's specific to my machine.
My first suspicion was that some library "hijacks" mlockall(), but calling the test program with `LD_DEBUG=all` shows that glibc gets called directly: 12248: symbol=mlockall; lookup in file=./test [0] 12248: symbol=mlockall; lookup in file=/lib/x86_64-linux-gnu/libc.so.6 [0] 12248: binding file ./test [0] to /lib/x86_64-linux-gnu/libc.so.6 [0]: normal symbol `mlockall' [GLIBC_2.2.5] An `strace` doesn't show anything meaningful (beside that mlockall's been called but never returns). dmesg and syslog don't show anything obvious (to me) as well.
Some information about the machine: - Intel(R) Core(TM) i7-6900K, Intel X99 chipset - NVMe 1.1b - 64GB RAM (4x 16GB)
I've also reverted all changes for sysctl and ld.conf and checked for other suspicious software without any luck.
I also tried a bunch of variations of the above program, but only `mlockall(MCL_CURRENT)` or `mlockall(MCL_FUTURE | MCL_CURRENT)` hang.
A `git diff v5.0..v5.1 mm/` doesn't show anything obvious (to me).
It seems, there's no debug/trace information that would help to find out what exactly it's doing.
I'm kinda lost at the moment.
PS: Variations of the above test program:
#include <stdio.h> #include <sys/mman.h> char foo[65536]; int main(char** argv) { printf("Before mlock()\n"); int e = mlock(foo, 8192); // works in 5.0, 5.1, 5.2, 5.3, 5.4 printf("After mlock()=%d\n", e); }
#include <stdio.h> #include <stdlib.h> #include <sys/mman.h> int main(char** argv) { printf("Before mlockall(MCL_FUTURE)\n"); int e = mlockall(MCL_FUTURE); // works in 5.0, 5.1, 5.2, 5.3, 5.4 printf("After mlockall(MCL_FUTURE) = %d\n", e); void* mem = malloc(1024 * 1024 * 1024); printf("After malloc()\n"); mem = malloc(1024 * 1024 * 1024); printf("After malloc()\n"); mem = malloc(1024 * 1024 * 1024); printf("After malloc()\n"); // works in 5.0, 5.1, 5.2, 5.3, 5.4 }
#include <stdio.h> #include <sys/mman.h> int main(char** argv) { printf("Before munlockall()\n"); int e = munlockall(); // works in 5.0, 5.1, 5.2, 5.3, 5.4 printf("After munlockall() = %d\n", e); }
#include <stdio.h> #include <sys/mman.h> int main(char** argv) { printf("Before mlockall(MCL_CURRENT|MCL_FUTURE)\n"); // works in 5.0 // hangs forever w/ 5.1 and newer int e = mlockall(MCL_CURRENT|MCL_FUTURE); printf("After mlockall(MCL_CURRENT|MCL_FUTURE) = %d\n", e); }
PPS: Kernel version images installed from https://kernel.ubuntu.com/~kernel-ppa/mainline/?C=N;O=D
-- Robert Stupp @snazy
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