linux-kernel - Re: [PATCH 1/1] signal: make group kill signal fatal

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Date:	Mon, 25 May 2009 18:21:55 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, ebiederm@...ssion.com,
	roland@...hat.com, linux-kernel@...r.kernel.org,
	Matthew Wilcox <matthew@....cx>
Subject: Re: [PATCH 1/1] signal: make group kill signal fatal

On 05/25/2009 02:07 AM, Oleg Nesterov wrote:
> On 05/24, Jiri Slaby wrote:
>>
>> __fatal_signal_pending() returns now true only for a non-group sent
>> sigkill, i. e. for example tgkill, send_sig...
> 
> No. Please look at complete_signal(). If we queue a fatal signal,
> we always add SIGKILL to any thread.

Ah, thanks. But it looks like it doesn't work well in some cases.
Consider this kernel code:

#include <linux/fs.h>
#include <linux/miscdevice.h>
#include <linux/module.h>
#include <linux/poll.h>
#include <linux/sched.h>

static int release(struct inode *ino, struct file *file)
{
        unsigned int a;
        printk(KERN_DEBUG "fst\n");
        for (a = 0; a < 10; a++) {
                printk(KERN_DEBUG "%s: SP=%u FSP=%u pend=%.16lx
shpend=%.16lx\n",
                                __func__,
                                signal_pending(current),
                                fatal_signal_pending(current),
                                current->pending.signal.sig[0],

current->signal->shared_pending.signal.sig[0]);
                if (fatal_signal_pending(current))
                        break;
                msleep(1000);
        }
        printk(KERN_DEBUG "done\n");
        return 0;
}

static DECLARE_WAIT_QUEUE_HEAD(wq);

static unsigned int poll(struct file *file, struct poll_table_struct *p)
{
        poll_wait(file, &wq, p);

        return 0;
}

static const struct file_operations fops = {
        .owner = THIS_MODULE,
        .release = release,
        .poll = poll,
};

static struct miscdevice m = {
        .minor = MISC_DYNAMIC_MINOR,
        .name = "m",
        .fops = &fops,
};

static int init1(void)
{
        return misc_register(&m);
}

static void exit1(void)
{
        misc_deregister(&m);
}

module_init(init1);
module_exit(exit1);

MODULE_LICENSE("GPL");






----------------------------------------------
And this user code:
#include <err.h>
#include <fcntl.h>
#include <poll.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>

int main(int argc, char **argv)
{
        struct pollfd fds = { .events = POLLIN };
        int fd;

        fd = open("/dev/m", O_RDONLY);
        if (fd < 0)
                err(1, "open");
        fds.fd = fd;
        if (poll(&fds, 1, -1) < 0)
                err(2, "poll");
        close(fd);
        return 0;
}






----------------------------------------------
It outputs:
fst
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
release: SP=1 FSP=0 pend=0000000000000000 shpend=0000000000000100
done

I.e. it won't get propagated to current->pending. Don't you have idea
why? If the poll isn't there, it works well.

glibc 2.9, x86_64
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