Re: Bug#285281: core dump on amd64 (gcc-3.4)

[Daniel Stekloff <dsteklof@us.ibm.com>]

On Wed, 2004-12-15 at 05:27, Kay Sievers wrote:
> On Wed, 2004-12-15 at 09:50 +0100, Marco d'Itri wrote:
> > clsdev->directory is NULL, is this a bug in libsysfs or udev?
> > Apparently this only happens on amd64.



This is definitely a libsysfs bug.



> > ----- Forwarded message from martin-deb@zero-based.org -----
> 
> > #0  0x0000000000403024 in sysfs_get_classdev_attr (clsdev=0x518260, name=0x40dcac "dev") at libsysfs/sysfs_class.c:643
> > 643             if (clsdev->directory->subdirs = NULL) 
> > (gdb) backtrace
> 
> It is caused by the vc class behavior, to emit events on every open()
> and close(). We get a lot of events on bootup for every vc device, cause
> it is several times reopened. This causes the sysfs-dir to go away while
> the device is opened in libsysfs. This simple test program:
> 
> #include <stdio.h>
> #include <unistd.h>
> #include <stddef.h>
> #include <stdlib.h>
> #include <string.h>
> #include <ctype.h>
> #include <errno.h>
> 
> #include "libsysfs/sysfs/libsysfs.h"
> 
> 
> int main(int argc, char *argv[], char *envp[])
> {
>         struct sysfs_class_device *class_dev;
>         struct sysfs_attribute *attr;
> 
>         mkdir("test-sys", 0775);
>         mkdir("test-sys/class", 0775);
>         mkdir("test-sys/class/test", 0775);
> 
>         setenv("SYSFS_PATH", "test-sys", 1);
> 
>         printf("open\n");
>         class_dev = sysfs_open_class_device_path("test-sys/class/test");
>         printf("%p\n", class_dev);
> 
>         printf("rmdir\n");
>         rmdir("test-sys/class/test");
> 
>         printf("read attr\n");
>         attr = sysfs_get_classdev_attr(class_dev, "dev");
> }
> 
> segfaults every time:
>   [kay@pim udev.kay]$ gcc -g -I libsysfs/sysfs -I libsysfs -o bug bug.c libsysfs/sysfs.a
>   [kay@pim udev.kay]$ ./bug 
>   open
>   0x804f0d8
>   rmdir
>   read attr
>   Segmentation fault
> 
> 
> This seems to fix it:
> 
> === libsysfs/sysfs_class.c 1.11 vs edited ==> --- 1.11/libsysfs/sysfs_class.c 2004-10-20 05:15:26 +02:00
> +++ edited/libsysfs/sysfs_class.c       2004-12-15 14:20:13 +01:00
> @@ -640,6 +640,9 @@
>                         return cur;
>         }
>  
> +       if (clsdev->directory = NULL)
> +               return NULL;
> +
>         if (clsdev->directory->subdirs = NULL) 
>                 if ((sysfs_read_dir_subdirs(clsdev->directory)) != 0 ||
>                     clsdev->directory->subdirs = NULL) 



We wrongly assume that the directory is there or is opened when
sysfs_get_classdev_attributes() runs prior to this. 

We'll apply this patch to the tree.

Thanks,

Dan


> 
> Thanks,
> Kay
> 
> 
> 
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