From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Subject: Re: [PATCH v2 1/2] sysfs: handle 'parent deleted before child added' Date: Fri, 6 Apr 2012 15:11:39 -0700 Message-ID: <20120406221139.GA22854@kroah.com> References: <20120406203619.22624.69445.stgit@dwillia2-linux.jf.intel.com> <20120406204514.GA20237@kroah.com> <20120406211711.GA12075@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: "Williams, Dan J" Cc: James Bottomley , linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org List-Id: linux-scsi@vger.kernel.org On Fri, Apr 06, 2012 at 02:44:37PM -0700, Williams, Dan J wrote: > On Fri, Apr 6, 2012 at 2:17 PM, Greg KH = 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 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 b= efore the > >> >> child is added have been observed. > >> >> > >> >> 1/ scsi is performing async scans and the device is removed pri= or to the > >> >> =A0 =A0async can thread running (can happen with an in-opportun= e / unlikely > >> >> =A0 =A0unplug 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 bee= n torn > >> >> =A0 =A0down (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=3Dlinux-scsi&m=3D133239707903443&w=3D2 > >> http://marc.info/?l=3Dlinux-scsi&m=3D133239709603452&w=3D2 > >> > >> > 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 th= e driver > >> > core, and I thought we had fixed all of these types of errors pr= operly. > >> > >> Hotplug lifetime rules are still transport specific. =A0So 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. =A0It turns a NULL > >> pointer crash into an explicit warning from kobject_add_internal. = =A0For > >> 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 figur= ed > >> it was worthwhile to post a patch to do the same for this 'parent > >> deleted' case. =A0But if crashing is the expectation then this pat= ch can > >> be dropped. > > > > No, crashing is not the expectation :) >=20 > I thought not, but sometimes the kernel likes to teach people that > bollix an api a hard lesson :). >=20 > > > > But, without that crash, would the above fixes ever have been notic= ed > > and fixed? =A0The device_add() most likely would have quietly faile= d and > > no one would have been the wiser. > > > > Or would something else have caused this to be an obvious problem? > > >=20 > 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. Ok, that's reasonable, I'll queue this up for 3.5. thanks, greg k-h