Re: libsysfs/udev hang

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

Hi Carl-Daniel,


On Tuesday 23 March 2004 03:55 am, Carl-Daniel Hailfinger wrote:
> Hi,
>
> while writing an ataraid replacement on top of device mapper, I stumbled
> upon a freeze in sysfs_close_device which only happens if udev is NOT
> compiled with DEBUG=true.
>
> Test routine (modified udevinfo function) follows:
> static int print_device_chain(const char *path)
> {
>         struct sysfs_class_device *class_dev;
>         struct sysfs_class_device *class_dev_parent;
>         struct sysfs_attribute *attr;
>         struct sysfs_device *sysfs_dev;
>         struct sysfs_device *sysfs_dev_parent;
>         struct dlist *cur_attrs;
>         int retval = 0;
>         unsigned int vendor,device,subsystem_vendor,subsystem_device;
>         unsigned long devsize;
>         unsigned char *buf;
>
>         /*  get the class dev */
>         class_dev = sysfs_open_class_device_path(path);
>         if (class_dev = NULL) {
>                 printf("couldn't get the class device\n");
>                 return -1;
>         }
>
>         cur_attrs = sysfs_get_classdev_attributes(class_dev);
>
>         /* get device size in 512 byte blocks from 'size' */
>         buf = sysfs_get_value_from_attributes(cur_attrs, "size");
>         devsize = strtoul(buf, NULL, 10);
>
>         /* read the 'dev' file for major/minor*/
>         buf = sysfs_get_value_from_attributes(cur_attrs, "dev");
>         printf("device '%s' has size %lu blocks and major:minor %s\n",
> class_dev->path, devsize, buf);
>
>         sysfs_close_list(cur_attrs);
>
>         /* get the device link (if parent exists look here) */
>         class_dev_parent = sysfs_get_classdev_parent(class_dev);
>         if (class_dev_parent != NULL) {
>                 class_dev = class_dev_parent;
>         }


First of all, you've opened a class_dev with an "open" call -> 
sysfs_open_class_device_path. This should have a matching "close" call to 
clean up the class device you've created. Instead, you assign the parent 
reference that's returned from a "get" call to class_dev. This isn't a good 
idea.

Second, you use a "get" function to retrieve a reference to the class_dev's 
attributes -> sysfs_get_classdev_attributes. Then you close the list using 
sysfs_close_list() rather than leaving that to the sysfs_close_classdev() 
function. 

Open functions in libsysfs create a device - and the memory for it - and 
return you the structure. These "open" functions must be followed with a 
"close" function to clean everything up.

Get functions are used on opened structures to return references to what you'd 
like to see like attributes or devices. They don't need to be "closed". 


>         sysfs_dev = sysfs_get_classdev_device(class_dev);
>         if (sysfs_dev != NULL)
>                 printf("follow the class device's \"device\"\n");
>
>         /* look the device chain upwards */
>         while (sysfs_dev != NULL) {
>
>                 printf("point1\n");
>                 /* open sysfs device directory and print all attributes */
>                 if (strcmp(sysfs_dev->bus, "pci") = 0) {
>                         cur_attrs = sysfs_get_device_attributes(sysfs_dev);
>                         buf = sysfs_get_value_from_attributes(cur_attrs,
> "vendor");
>                         vendor = (unsigned int)strtoul(buf + 2, NULL, 16);
>                         buf = sysfs_get_value_from_attributes(cur_attrs,
> "device");
>                         device = (unsigned int)strtoul(buf + 2, NULL, 16);
>                         buf = sysfs_get_value_from_attributes(cur_attrs,
> "subsystem_vendor");
>                         subsystem_vendor = (unsigned int)strtoul(buf + 2,
> NULL, 16);
>                         buf = sysfs_get_value_from_attributes(cur_attrs,
> "subsystem_device");
>                         subsystem_device = (unsigned int)strtoul(buf + 2,
> NULL, 16);
>                         sysfs_close_list(cur_attrs);


Here's where you close a list that you received through a "get" call. You 
shouldn't call close on references you receive with "get" functions.


>                         printf("device '%s' has vendor %x device %x
> subvendor %x subdevice %x\n",
>                                  class_dev->path, vendor, device,
> subsystem_vendor, subsystem_device);
>                         printf("point2\n");
>                         break;
>                 }
>                 printf("point3\n");
>
>                 sysfs_dev_parent = sysfs_get_device_parent(sysfs_dev);
>                 printf("point4\n");
>                 if (sysfs_dev_parent = NULL)
>                         break;
>                 printf("point5\n");
>
>                 sysfs_dev = sysfs_dev_parent;
>                 printf("point6\n");
>         }
>         printf("point7\n");
>         sysfs_close_device(sysfs_dev);


Here's where you close a reference you received through a "get" call. 



>         printf("point8\n");
> exit:
>         return retval;
> }
>
>
> And if I compile udev with DEBUG=true, it works perfectly. If I compile
> udev without debugging, it hangs between point7 and point8.
>
> Did I make any mistakes in the above routine which trigger the hang? I ask
> here because the libsysfs version in udev differs from libsysfs 1.0.0.


I will create a similar routine, using correct libsysfs formats, and see if I 
run into a race.

Please let me know if this helps or if I can explain further. 

Thanks,

Dan



> Regards,
> Carl-Daniel



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