Re: [PATCH v2 1/2] sysfs: handle 'parent deleted before child added'
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On Fri, Apr 6, 2012 at 2:17 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Apr 06, 2012 at 02:06:50PM -0700, Williams, Dan J wrote: >> On Fri, Apr 6, 2012 at 1:45 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: >> > On Fri, Apr 06, 2012 at 01:41:06PM -0700, Dan Williams wrote: >> >> In scsi at least two cases of the parent device being deleted before the >> >> child is added have been observed. >> >> >> >> 1/ scsi is performing async scans and the device is removed prior to the >> >> async can thread running (can happen with an in-opportune / unlikely >> >> unplug during initial scan). >> > >> > That sounds like a bug in the scsi code, doesn't it? >> > >> >> 2/ libsas discovery event running after the parent port has been torn >> >> down (this is a bug in libsas). >> > >> > Is this fixed somewhere? >> >> Yes, these two issues have pending fixes that are posted to linux-scsi: >> >> http://marc.info/?l=linux-scsi&m=133239707903443&w=2 >> http://marc.info/?l=linux-scsi&m=133239709603452&w=2 >> >> > I don't want to paper over bugs like this by changing the sysfs core. >> > We went through this a lot years ago when scsi changed to use the driver >> > core, and I thought we had fixed all of these types of errors properly. >> >> Hotplug lifetime rules are still transport specific. So in this case >> scsi-core is innocent these are bugs from libsas and >> scsi_transport_sas. > > Ok, thanks for the explaination. > >> > So, any chance to fix these properly as well? >> >> This patch doesn't really paper over anything. It turns a NULL >> pointer crash into an explicit warning from kobject_add_internal. For >> the libsas/scsi case this device_add() failure is still fatal. >> Regardless of whether sysfs changes the above two fixes are still >> required. >> >> Since the -EEXIST case is just a KERN_ERR and not a BUG_ON I figured >> it was worthwhile to post a patch to do the same for this 'parent >> deleted' case. But if crashing is the expectation then this patch can >> be dropped. > > No, crashing is not the expectation :) I thought not, but sometimes the kernel likes to teach people that bollix an api a hard lesson :). > > But, without that crash, would the above fixes ever have been noticed > and fixed? The device_add() most likely would have quietly failed and > no one would have been the wiser. > > Or would something else have caused this to be an obvious problem? > We still have the big red flag dump_stack() in kobject_add_internal() (which patch 2 turns into a real WARN()), and for scsi our hotplug tests still crash later on because libsas makes assumptions about the device path. I understand the paranoia here, "check for NULL" is usually a band-aid, but in this case this is just a softer introduction to a debug session. No less vocal than before as far as I can see. -- Dan -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html