Problem delivering signals while blocked in recvfrom

[David Preece <davep@pscope.net>]

Hi,

As per the subject, I have a single threaded process blocked collecting 
UDP packets in recvfrom and I'm attempting to send it SIGHUP. No matter 
what I do I get a segfault within the libc6. I've tried both the GNU 
and BSD styles of signal handling, and within those have set flags for 
both "fail the recvfrom" and "resume it", to no avail.

There's not a lot of complication involved in the crash:



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(gdb) run
Starting program: /home/davep/pscope/tcom/flowlogd/flowlogd/flowlogd

Program received signal SIGHUP, Hangup.
0x4039c276 in recvfrom () from /lib/libc.so.6



There's a simple test case too. Compile and run this (c++), then send 
it a SIGHUP. I know I've not put a handler in at all yet, it doesn't 
need it in order to demonstrate the crash.



#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h> //for bzero
#include <signal.h>

int main (int argc, char * const argv[])
{
    //create and bind
	int sockfd=socket(AF_INET,SOCK_DGRAM,0);
	sockaddr_in servaddr;
	bzero(&servaddr,sizeof(sockaddr_in));
	servaddr.sin_family=AF_INET;
	servaddr.sin_addr.s_addr=htonl(INADDR_ANY);
	servaddr.sin_port=htons(1234);
	bind(sockfd,(sockaddr*)&servaddr,sizeof(sockaddr_in));
	//get a packet
	char packet[8192];
	sockaddr_in cliaddr;
	socklen_t fromlen=sizeof(sockaddr_in);
	recvfrom(sockfd,packet,8191,0,(sockaddr*)&cliaddr,&fromlen);
	printf("Would be nice if recvfrom returned, eh?\n");
};



Am I missing something here? Any ideas what I can do?

Regards,
David Preece