On Thu 11-12-14 00:21:09, KY Srinivasan wrote: > > > > -----Original Message----- > > From: Michal Hocko [mailto:mhocko@xxxxxxx] > > Sent: Tuesday, December 9, 2014 2:56 AM > > To: Yasuaki Ishimatsu > > Cc: KY Srinivasan; gregkh@xxxxxxxxxxxxxxxxxxx; linux- > > kernel@xxxxxxxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; olaf@xxxxxxxxx; > > apw@xxxxxxxxxxxxx; linux-mm@xxxxxxxxx > > Subject: Re: [PATCH 2/2] Drivers: hv: balloon: Fix the deadlock issue in the > > memory hot-add code > > > > On Tue 09-12-14 19:25:50, Yasuaki Ishimatsu wrote: > > > (2014/12/09 18:08), Michal Hocko wrote: > > [...] > > > >Doesn't udev retry the operation if it gets EBUSY or EAGAIN? > > > > > > It depend on implementation of udev.rules. So we can retry > > > online/offline operation in udev.rules. > > [...] > > > > # Memory hotadd request > > SUBSYSTEM=="memory", ACTION=="add", > > DEVPATH=="/devices/system/memory/memory*[0-9]", > > TEST=="/sys$devpath/state", RUN+="/bin/sh -c 'echo online > > > /sys$devpath/state'" > > > > OK so this is not prepared for a temporary failures and retries. > > > > > >And again, why cannot we simply make the onlining fail or try_lock > > > >and retry internally if the event consumer cannot cope with errors? > > > > > > Did you mean the following Srinivasan's first patch looks good to you? > > > https://lkml.org/lkml/2014/12/2/662 > > > > Heh, I was just about to post this. Because I haven't noticed the previous > > patch yet. Yeah, Something like that. Except that I would expect EAGAIN or > > EBUSY rather than ERESTARTSYS which should never leak into userspace. And > > that would happen here AFAICS because signal_pending will not be true > > usually. > Michal, > > I agree that the fix to this problem must be outside the clients > of add_memory() and that is the reason I had sent that patch: > https://lkml.org/lkml/2014/12/2/662. Let me know if you want me to > resend this patch with the correct return value. Please think about the other suggested options as well. > Regards, > > K. Y > > > > So there are two options. Either make the udev rule more robust and retry > > within RUN section or do the retry withing online_pages (try_lock and go into > > interruptible sleep which gets signaled by finished add_memory()). The later > > option is safer wrt. the userspace because the operation wouldn't fail > > unexpectedly. > > Another option would be generating the sysfs file after all the internal > > initialization is done and call it outside of the memory hotplug lock. > > > > -- > > Michal Hocko > > SUSE Labs -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>