[LTP] [PATCH] syscalls/munmap04: Stop using MAP_FIXED_NOREPLACE

[Ricardo B. Marlière]

On Mon Jul 28, 2025 at 10:39 AM -03, Cyril Hrubis wrote:
> Hi!
>> On some machines, mmap() call might return MAP_FAILED when passed the
>> MAP_FIXED_NOREPLACE flag for reasons other than what the test expect: vma
>> limit reached. While at it, add a sanity check if no regions were mapped.
>> 
>> Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
>> ---
>>  testcases/kernel/syscalls/munmap/munmap04.c | 8 ++++----
>>  1 file changed, 4 insertions(+), 4 deletions(-)
>> 
>> diff --git a/testcases/kernel/syscalls/munmap/munmap04.c b/testcases/kernel/syscalls/munmap/munmap04.c
>> index e046d17a75f8f75c5b11d569c33da41d7adc7d09..f55aa770a99d2facb53234fa593fa3f41a16cb00 100644
>> --- a/testcases/kernel/syscalls/munmap/munmap04.c
>> +++ b/testcases/kernel/syscalls/munmap/munmap04.c
>> @@ -37,8 +37,7 @@ static void setup(void)
>>  
>>  	while (1) {
>>  		void *p = mmap((void *)(base + PAD * vma_size * map_count),
>> -			     vma_size, PROT_NONE,
>> -			     MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED_NOREPLACE,
>> +			     vma_size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS,
>
> How do we avoid the adjacent mapping merges without the
> MAP_FIXED_NOREPLACE flag? With the flag we force particular addresses
> that have padding between then. Without the flag kernel is free to place
> the mappings anywhere it wants, e.g. create a big continous mapping in
> which case we would effectively have a signle vma in the kernel.
>
>
>
>>  			     -1, 0);
>>  		if (p == MAP_FAILED)
>>  			break;
>
> Sholdn't it be easier to continue; here if errno == EEXIST? that would
> mean that we would not map over any mappings that exists in the process
> address space and continue retrying with increasing addresses:
>
> 	if (p == MAP_FAILED && errno == EEXIST)
> 		continue;
>
> 	if (p == MAP_FAILED)
> 		break;
>
> 	maps[map_count++] = p;

Indeed, many thanks for the suggestion! Will send v2

>
>> @@ -46,8 +45,9 @@ static void setup(void)
>>  	}
>>  
>>  	if (map_count == MAP_MAX_COUNT)
>> -		tst_brk(TBROK, "Mapped all %d regions, expected less",
>> -			map_count);
>> +		tst_brk(TBROK, "Mapped all %d regions, expected less", map_count);
>> +	if (map_count == 0)
>> +		tst_brk(TBROK, "Mapped 0 regions");
>>  
>>  	tst_res(TINFO, "Mapped %d regions", map_count);
>>  }
>> 
>> ---
>> base-commit: 6af619552ce7676171e47b88964ffb5b08499b36
>> change-id: 20250728-fixes-munmap04-02083c550c6b
>> 
>> Best regards,
>> -- 
>> Ricardo B. Marlière <rbm@suse.com>
>> 
>> 
>> -- 
>> Mailing list info: https://lists.linux.it/listinfo/ltp