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SubjectRe: 2.6.x signal handler bug
On Sat, 26 June 2004 02:56:51 +0300, Paul Maurides wrote:
>
> The bug has been reproduced successfully using the following program
> on kernel 2.6.5 and 2.6.7, and probably affects any other 2.6 kernel.

All, since about 2.5.71 or so.

> Kernel 2.4 produce the correct behavior, an endless loop of handled
> signals, but on kernel 2.6 the program segfaults.

The program never returns from it's signal handler. Instead, it
causes yet another segfault. Any program stupid enough to cause a
segfault inside the segfault handler, should be killed. Full stop.

> #include <signal.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <setjmp.h>
>
> volatile int len;
> volatile int real;
> volatile int caught;
> jmp_buf env;
>
> void catcher(int sig){
> signal(SIGSEGV,catcher);
> printf("requested: %9d malloced: %9d\n",len,real);
> longjmp(env, 1);
> }
>
> int main(){
> char* p=0;
> len = 0;
> signal(SIGSEGV,catcher);
>
> setjmp(env);
> len++;
> free(p);
> p = malloc(len);
> real = 0;
> while(1){
> p[real] = 0;
> real++;
> }
> return 0;
> }

Jörn

--
Fancy algorithms are buggier than simple ones, and they're much harder
to implement. Use simple algorithms as well as simple data structures.
-- Rob Pike
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