Re: mmap, SIGBUS, and handling it

[Alex Riesen <Alexander.Riesen@synopsys.com>]

On Fri, May 10, 2002 at 07:04:36PM +0300, Mihai RUSU wrote:
> On Fri, 10 May 2002, David S. Miller wrote:
> 
> >    From: Mihai RUSU <dizzy@roedu.net>
> >    Date: Fri, 10 May 2002 18:37:21 +0300 (EEST)
> >
> >    PS: why signal(SIGBUS,SIG_IGN) doesnt work, but a user handler its called
> >    if set with signal(SIGBUS,handle_sigbus) ?
> >
> > How would you like the kernel to "ignore" a page fault that cannot be
> > serviced?
> >
> 
> You are right, its not that I want to ignore it. The problem was that I
> want to handle it some way but I dont know how. If I will make a user
> handler for it how can I know if its a SIGBUS from a HW error or a SIGBUS
> from that write()-case. Because I have to continue serving files even
> after received a SIGBUS in that write (otherwise my file server will exit
> with SIGBUS and thats no good :) ).
> 
> Take for example any single process ftp/http server, they are hit by this
> problem. Which solution would you recommend ? :)
> 

Just take a closer look on sigaction(2). The field sa_sigaction and
flags SA_SIGINFO in sa_flags can help to identify the source of the
SIGBUS.

SIGACTION(2)        Linux Programmer's Manual        SIGACTION(2)
...
       the  sender  of  the  POSIX.1b  signal.   SIGILL,  SIGFPE,
       SIGSEGV and SIGBUS fill in si_addr with the address of the
       fault.  SIGPOLL fills in si_band and si_fd.
...
       si_code indicates why this  signal  was  sent.   It  is  a
       value,  not  a bitmask.  The values which are possible for
       any signal are listed in this table:
...
       |                  SIGBUS                    |
       +-----------+--------------------------------+
       |BUS_ADRALN | invalid address alignment      |
       +-----------+--------------------------------+
       |BUS_ADRERR | non-existent physical address  |
       +-----------+--------------------------------+
       |BUS_OBJERR | object specific hardware error |


-alex