linux-kernel - Re: [PATCH 2/4] selftests/sigaltstack: Fix the sas test on old kernels

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Date:	Sun, 8 May 2016 18:32:34 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Stas Sergeev <stsp@...t.ru>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Shuah Khan <shuahkh@....samsung.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Brian Gerst <brgerst@...il.com>,
	Linux API <linux-api@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/4] selftests/sigaltstack: Fix the sas test on old kernels

On May 7, 2016 8:02 AM, "Stas Sergeev" <stsp@...t.ru> wrote:
>
> 03.05.2016 20:31, Andy Lutomirski пишет:
>
>> The handling for old kernels was wrong.  Fix it.
>>
>> Reported-by: Ingo Molnar <mingo@...nel.org>
>> Cc: Stas Sergeev <stsp@...t.ru>
>> Cc: Al Viro <viro@...iv.linux.org.uk>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: Andy Lutomirski <luto@...capital.net>
>> Cc: Borislav Petkov <bp@...en8.de>
>> Cc: Brian Gerst <brgerst@...il.com>
>> Cc: Denys Vlasenko <dvlasenk@...hat.com>
>> Cc: H. Peter Anvin <hpa@...or.com>
>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>> Cc: Oleg Nesterov <oleg@...hat.com>
>> Cc: Pavel Emelyanov <xemul@...allels.com>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Shuah Khan <shuahkh@....samsung.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: linux-api@...r.kernel.org
>> Cc: linux-kernel@...r.kernel.org
>> Signed-off-by: Andy Lutomirski <luto@...nel.org>
>> ---
>>   tools/testing/selftests/sigaltstack/sas.c | 21 ++++++++++++++-------
>>   1 file changed, 14 insertions(+), 7 deletions(-)
>>
>> diff --git a/tools/testing/selftests/sigaltstack/sas.c b/tools/testing/selftests/sigaltstack/sas.c
>> index 57da8bfde60b..a98c3ef8141f 100644
>> --- a/tools/testing/selftests/sigaltstack/sas.c
>> +++ b/tools/testing/selftests/sigaltstack/sas.c
>> @@ -15,6 +15,7 @@
>>   #include <alloca.h>
>>   #include <string.h>
>>   #include <assert.h>
>> +#include <errno.h>
>>     #ifndef SS_AUTODISARM
>>   #define SS_AUTODISARM  (1 << 4)
>> @@ -117,13 +118,19 @@ int main(void)
>>         stk.ss_flags = SS_ONSTACK | SS_AUTODISARM;
>>         err = sigaltstack(&stk, NULL);
>>         if (err) {
>> -               perror("[FAIL]\tsigaltstack(SS_ONSTACK | SS_AUTODISARM)");
>> -               stk.ss_flags = SS_ONSTACK;
>> -       }
>> -       err = sigaltstack(&stk, NULL);
>> -       if (err) {
>> -               perror("[FAIL]\tsigaltstack(SS_ONSTACK)");
>> -               return EXIT_FAILURE;
>> +               if (errno == EINVAL) {
>> +                       printf("[NOTE]\tThe running kernel doesn't support SS_AUTODISARM\n");
>> +                       /*
>> +                        * If test cases for the !SS_AUTODISARM variant were
>> +                        * added, we could still run them.  We don't have any
>> +                        * test cases like that yet, so just exit and report
>> +                        * success.
>> +                        */
>
> But that was the point, please see how it handles the
> old kernels:
>
> $ ./sas
> [FAIL]    sigaltstack(SS_ONSTACK | SS_AUTODISARM): Invalid argument
> [RUN]    signal USR1
> [FAIL]    ss_flags=1, should be SS_DISABLE
> [RUN]    switched to user ctx
> [RUN]    signal USR2
> [FAIL]    sigaltstack re-used
> [FAIL]    Stack corrupted
> [RUN]    Aborting

This is useful as a demonstration of why the feature is useful, but it
doesn't indicate that anything is wrong with old kernels per she.
That's why I changed it to simply report that the feature is missing.