Re: [libsas PATCH v12 04/11] sysfs: handle 'parent deleted before child added'

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On Thu, Mar 22, 2012 at 7:39 AM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, Mar 21, 2012 at 11:32:14PM -0700, Dan Williams wrote:
[..]
>> diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
>> index 7fdf6a7..86521ee 100644
>> --- a/fs/sysfs/dir.c
>> +++ b/fs/sysfs/dir.c
>> @@ -714,6 +714,9 @@ int sysfs_create_dir(struct kobject * kobj)
>>       else
>>               parent_sd = &sysfs_root;
>>
>> +     if (!parent_sd)
>> +             return -ENOENT;
>> +
>>       if (sysfs_ns_type(parent_sd))
>>               ns = kobj->ktype->namespace(kobj);
>>       type = sysfs_read_ns_type(kobj);
>
> So what happens if this is true?  Does this patch fix the oops?

This patch downgrades the oops by turning it into a device_add()
failure, but the patches that *fix* this warning are here [1] and here
[2].

> What kernels should this be applied to where this problem has been seen?

I assume this has been a latent problem ever since scsi async scanning
was added (2.6.20-rc2), but it's a rare corner case to unplug devices
during the initial scan.

>> diff --git a/lib/kobject.c b/lib/kobject.c
>> index c33d7a1..e5f86c0 100644
>> --- a/lib/kobject.c
>> +++ b/lib/kobject.c
>> @@ -192,13 +192,14 @@ static int kobject_add_internal(struct kobject *kobj)
>>
>>               /* be noisy on error issues */
>>               if (error == -EEXIST)
>> -                     printk(KERN_ERR "%s failed for %s with "
>> +                     pr_err("%s failed for %s with "
>>                              "-EEXIST, don't try to register things with "
>>                              "the same name in the same directory.\n",
>>                              __func__, kobject_name(kobj));
>>               else
>> -                     printk(KERN_ERR "%s failed for %s (%d)\n",
>> -                            __func__, kobject_name(kobj), error);
>> +                     pr_err("%s failed for %s (error: %d parent: %s)\n",
>> +                            __func__, kobject_name(kobj), error,
>> +                            parent ? kobject_name(parent) : "'none'");
>>               dump_stack();
>>       } else
>>               kobj->state_in_sysfs = 1;
>
> These changes have nothing to do with the above fix, so why include them
> here?

It wasn't until I realized which 'parent' and which 'child' were
interacting that I was able to identify the real fixes.  Since it was
helpful for the scsi/sas case, I decided to leave the more informative
warning for the next person that gets to debug a similar failure.

> And note, I hate pr_err(), what's wrong with printk() in this instance?

This is a bit circuitous, but extending the warning to include the
'parent' and 'child' pushed up against 80 columns and since this
routine has a pr_debug() a few lines up I thought a pr_ conversion was
acceptable.  The pr_err() conversion of the EEXIST case just came
along for the ride to keep the print style consistent (at least in
this routine).

--
Dan

[1]: http://marc.info/?l=linux-scsi&m=133239707903443&w=2
[2]: http://marc.info/?l=linux-scsi&m=133239709603452&w=2
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