Re: [LTP] [PATCH v2] overcommit_memory: Fix integer overflow and 32-bit limits

[Petr Vorel <pvorel@suse.cz>]

> The overcommit test uses sum_total, the sum (memory and swap) to test
> the overcommit settings.

> This fixes two problems on 32-bit systems. The first is seen with a
> integer overflow can occur when calculating sum_total * 2, if the
> sum_total is larger than 2GB. The second is limited virtual address

You still mention GB ...

> space (2-3GB) means the test can fail from address space exhaustion
> before overcommit has been tested.

> Now the test runs correctly on low-memory 32-bit systems while avoiding
> both the overflow bug and virtual address space issues.

> Signed-off-by: Ben Copeland <ben.copeland@linaro.org>
> Acked-by: Arnd Bergmann <arnd@arndb.de>
> Reviewed-by: Petr Vorel <pvorel@suse.cz>
> ---
>  .../kernel/mem/tunable/overcommit_memory.c    | 33 +++++++++++++++----
>  1 file changed, 27 insertions(+), 6 deletions(-)

> diff --git a/testcases/kernel/mem/tunable/overcommit_memory.c b/testcases/kernel/mem/tunable/overcommit_memory.c
> index 9b2cb479d..7ff5a98d0 100644
> --- a/testcases/kernel/mem/tunable/overcommit_memory.c
> +++ b/testcases/kernel/mem/tunable/overcommit_memory.c
> @@ -131,24 +131,45 @@ static void overcommit_memory_test(void)
>  	TST_SYS_CONF_LONG_SET(OVERCOMMIT_MEMORY, 2, 1);

>  	update_mem_commit();
> -	alloc_and_check(commit_left * 2, EXPECT_FAIL);
> -	alloc_and_check(commit_limit + total_batch_size, EXPECT_FAIL);
> +	/* Skip tests that would overflow or exceed 32-bit address space */
> +	if (tst_kernel_bits() == 64 || (unsigned long)commit_left <= TST_GB / TST_KB) {

... but TST_GB / TST_KB is actually MB (you could use TST_MB).

Yes, this fixes the problem on i686 as the tests are skipped as sum_total is
smaller than 1MB.

Kind regards,
Petr

tst_kernel.c:90: TINFO: uname.machine=i686 kernel is 32bit
tst_test.c:2021: TINFO: LTP version: 20250930
tst_test.c:2024: TINFO: Tested kernel: 6.17.1-1-default #1 SMP PREEMPT_DYNAMIC Tue Oct  7 04:26:30 UTC 2025 (1bf5c2e) i686
tst_kconfig.c:88: TINFO: Parsing kernel config '/proc/config.gz'
tst_kconfig.c:676: TINFO: CONFIG_FAULT_INJECTION kernel option detected which might slow the execution
tst_test.c:1842: TINFO: Overall timeout per run is 0h 02m 00s
overcommit_memory.c:104: TINFO: MemTotal is 2050308 kB
overcommit_memory.c:106: TINFO: SwapTotal is 2098152 kB
overcommit_memory.c:110: TINFO: CommitLimit is 3121256 kB
overcommit_memory.c:123: TINFO: Setting /proc/sys/vm/overcommit_ratio to 30
overcommit_memory.c:126: TINFO: TotalBatchSize is 8008 kB
overcommit_memory.c:132: TINFO: Setting /proc/sys/vm/overcommit_memory to 2
overcommit_memory.c:140: TCONF: Skipping large allocation tests due to address space limits
overcommit_memory.c:146: TCONF: Skipping commit_left/2 allocation test due to address space limits
overcommit_memory.c:150: TINFO: Setting /proc/sys/vm/overcommit_memory to 0
overcommit_memory.c:152: TINFO: ONE_GB: 1073741824
overcommit_memory.c:153: TINFO: TST_GB: 1073741824
overcommit_memory.c:154: TINFO: TST_MB: 1048576
overcommit_memory.c:155: TINFO: TST_GB / TST_KB: 1048576
overcommit_memory.c:156: TINFO: TST_MB * 1024: 1073741824
overcommit_memory.c:157: TINFO: tst_kernel_bits(): 32
overcommit_memory.c:158: TINFO: (unsigned long)sum_total <= ONE_GB: 1
overcommit_memory.c:159: TINFO: (unsigned long)sum_total <= TST_GB: 1
overcommit_memory.c:160: TINFO: condition: 1
overcommit_memory.c:193: TINFO: malloc 1669706 kB successfully
overcommit_memory.c:212: TPASS: alloc passed as expected
overcommit_memory.c:171: TCONF: Skipping large allocation test due to address space limits
overcommit_memory.c:175: TINFO: Setting /proc/sys/vm/overcommit_memory to 1
overcommit_memory.c:193: TINFO: malloc 2074230 kB successfully
overcommit_memory.c:212: TPASS: alloc passed as expected
overcommit_memory.c:182: TCONF: Skipping large allocation tests due to address space limits


> +		alloc_and_check(commit_left * 2, EXPECT_FAIL);
> +		alloc_and_check(commit_limit + total_batch_size, EXPECT_FAIL);
> +	} else {
> +		tst_res(TCONF, "Skipping large allocation tests due to address space limits");
> +	}
>  	update_mem_commit();
> -	alloc_and_check(commit_left / 2, EXPECT_PASS);
> +	if (tst_kernel_bits() == 64 || (unsigned long)commit_left <= TST_GB / TST_KB) {
> +		alloc_and_check(commit_left / 2, EXPECT_PASS);
> +	} else {
> +		tst_res(TCONF, "Skipping commit_left/2 allocation test due to address space limits");
> +	}

>  	/* start to test overcommit_memory=0 */
>  	TST_SYS_CONF_LONG_SET(OVERCOMMIT_MEMORY, 0, 1);

>  	update_mem();
>  	alloc_and_check(free_total / 2, EXPECT_PASS);
> -	alloc_and_check(sum_total * 2, EXPECT_FAIL);
> +	/* Skip if sum_total * 2 would exceed address space.
> +	 * On 32-bit, skip when sum_total > ULONG_MAX/4 (~1GB).
> +	 * Most 32-bit systems with <=1GB RAM can map 2x that in 3GB vaddr space.
> +	 * Systems with 2GB+ RAM likely cannot fit allocations in vaddr space. */
> +	if (tst_kernel_bits() == 64 || (unsigned long)sum_total <= TST_GB / TST_KB) {
> +		alloc_and_check(sum_total * 2, EXPECT_FAIL);
> +	} else {
> +		tst_res(TCONF, "Skipping large allocation test due to address space limits");
> +	}

>  	/* start to test overcommit_memory=1 */
>  	TST_SYS_CONF_LONG_SET(OVERCOMMIT_MEMORY, 1, 1);

>  	alloc_and_check(sum_total / 2, EXPECT_PASS);
> -	alloc_and_check(sum_total, EXPECT_PASS);
> -	alloc_and_check(sum_total * 2, EXPECT_PASS);
> +	if (tst_kernel_bits() == 64 || (unsigned long)sum_total <= TST_GB / TST_KB) {
> +		alloc_and_check(sum_total, EXPECT_PASS);
> +		alloc_and_check(sum_total * 2, EXPECT_PASS);
> +	} else {
> +		tst_res(TCONF, "Skipping large allocation tests due to address space limits");
> +	}

>  }

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