[LTP] hugemmap34 trigger oom if compile with CFLAGS='-fstack-clash-protection'

[Jan Stancek]

On Wed, Feb 5, 2025 at 3:54 AM Wei Gao <wegao@suse.com> wrote:
>
> Hi Jan
>
> Compiling hugemmap34 with CFLAGS='-fstack-clash-protection' causes gcc to insert additional stack address validation checks during alloca calls.  This results in kernel start allocate memory really , eventually triggering an OOM.
>
> In our normal openqa env we do not have such big memory(1024GB) to support this test. So we
>  have to disable CFLAGS='-fstack-clash-protection' if we still need this case running in our env.

Hi,

It sounds like you already found the cause. We seem to have couple choices:

1) strip the option from the CFLAGS for this testcase
diff --git a/testcases/kernel/mem/hugetlb/hugemmap/Makefile
b/testcases/kernel/mem/hugetlb/hugemmap/Makefile
index 2d651b4aa..1154ab3de 100644
--- a/testcases/kernel/mem/hugetlb/hugemmap/Makefile
+++ b/testcases/kernel/mem/hugetlb/hugemmap/Makefile
@@ -8,4 +8,7 @@ include $(top_srcdir)/include/mk/testcases.mk
 include $(abs_srcdir)/../Makefile.inc
 include $(top_srcdir)/include/mk/generic_leaf_target.mk

+CFLAGS_no_stack_prot := $(filter-out -fstack-clash-protection, $(CFLAGS))
+
+hugemmap34: CFLAGS=$(CFLAGS_no_stack_prot)

2) increase the memory requirements for the test.

I'd probably go with 1) since we want kernel to catch any issues anyway. And it
allows test to run on larger pool of systems.

>
> ===log with CFLAGS='-fstack-clash-protection'===
> [71073.562094] [T13546] oom-kill:constraint=CONSTRAINT_NONE,nodemask=(null),cpuset=/,mems_allowed=0-1,global_oom,task_memcg=/,task=hugemmap34,pid=13542,uid=0
> [71073.562109] [T13546] Out of memory: Killed process 13542 (hugemmap34) total-vm:4764864kB, anon-rss:2816000kB, file-rss:0kB, shmem-rss:0kB, UID:0 pgtables:636kB oom_score_adj:0
>
> tst_hugepage.c:84: TINFO: 1 hugepage(s) reserved
> tst_tmpdir.c:317: TINFO: Using /tmp/LTP_hug2vxfh1 as tmpdir (btrfs filesystem)
> tst_test.c:1097: TINFO: Mounting none to /tmp/LTP_hug2vxfh1/hugetlbfs fstyp=hugetlbfs flags=0
> tst_test.c:1900: TINFO: LTP version: 20240930
> tst_test.c:1904: TINFO: Tested kernel: 6.4.0-150700.40-default #1 SMP Thu Jan 9 12:43:31 UTC 2025 (f78fd5e) ppc64le
> tst_kconfig.c:88: TINFO: Parsing kernel config '/proc/config.gz'
> tst_kconfig.c:669: TINFO: CONFIG_LATENCYTOP kernel option detected which might slow the execution
> tst_test.c:1724: TINFO: Overall timeout per run is 0h 02m 00s
> hugemmap34.c:152: TINFO: searching for huge page and child stack placement
> hugemmap34.c:175: TINFO: potential stack at address 0x7effff000000
> hugemmap34.c:192: TINFO: stack = 0x7effff000000-0x7f0000000000, hugepage = 0x7dffff000000-0x7e0000000000
> tst_coredump.c:32: TINFO: Avoid dumping corefile for process(pid=20714)
> hugemmap34.c:56: TINFO: Child process starting with top of stack at 0x7effffffff80
>
> tst_test.c:1785: TINFO: Killed the leftover descendant processes
> tst_test.c:1792: TINFO: If you are running on slow machine, try exporting LTP_TIMEOUT_MUL > 1
> tst_test.c:1793: TBROK: Test killed! (timeout?)
>
>
> ===log without CFLAGS='-fstack-clash-protection'===
> tst_hugepage.c:84: TINFO: 1 hugepage(s) reserved
> tst_tmpdir.c:317: TINFO: Using /tmp/LTP_hugjztvoX as tmpdir (btrfs filesystem)
> tst_test.c:1097: TINFO: Mounting none to /tmp/LTP_hugjztvoX/hugetlbfs fstyp=hugetlbfs flags=0
> tst_test.c:1900: TINFO: LTP version: 20240930
> tst_test.c:1904: TINFO: Tested kernel: 6.4.0-150700.40-default #1 SMP Thu Jan 9 12:43:31 UTC 2025 (f78fd5e) ppc64le
> tst_kconfig.c:88: TINFO: Parsing kernel config '/proc/config.gz'
> tst_kconfig.c:669: TINFO: CONFIG_LATENCYTOP kernel option detected which might slow the execution
> tst_test.c:1724: TINFO: Overall timeout per run is 0h 02m 00s
> hugemmap34.c:152: TINFO: searching for huge page and child stack placement
> hugemmap34.c:175: TINFO: potential stack at address 0x7effff000000
> hugemmap34.c:192: TINFO: stack = 0x7effff000000-0x7f0000000000, hugepage = 0x7dffff000000-0x7e0000000000
> tst_coredump.c:32: TINFO: Avoid dumping corefile for process(pid=20704)
> hugemmap34.c:56: TINFO: Child process starting with top of stack at 0x7effffffff80
> hugemmap34.c:77: TINFO: Child process extended stack up to 0x7dfffffeff80, hasn't reached 0x7dffeffeff80
> hugemmap34.c:79: TPASS: Child killed by SIGSEGV as expected
>
> Thanks.
> Regards
> Gao Wei
>