On Thu, Dec 08, 2022 at 09:00:17AM +0100, Stephen Kitt wrote: > Hi Bjorn, > > On Wed, 7 Dec 2022 15:56:08 -0600, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > On Thu, Oct 06, 2022 at 01:59:50PM +0200, Stephen Kitt wrote: > > > In pcie_aspm_init_link_state(), a number of checks are made to > > > determine whether the function should proceed, before the result of > > > the call to pcie_aspm_sanity_check() is actually used. The latter > > > function doesn't change any state, it only reports a result, so > > > calling it later doesn't make any difference to the state of the > > > devices or the information we have about them. But having the call > > > early reportedly can cause null-pointer dereferences; see > > > https://unix.stackexchange.com/q/322337 for one example with > > > pcie_aspm=off (this was reported in 2016, but the relevant code hasn't > > > changed since then). > > > > Thanks, Stephen! > > > > That stackexchange report doesn't have much information, but it looks > > similar to this old report from Jan Rueth, which I'm sorry to say I > > never got resolved: > > > > https://bugzilla.kernel.org/show_bug.cgi?id=187731 > > https://lore.kernel.org/all/4cec62c2-218a-672b-8c12-d44e8df56aae@xxxxxxxxxxxxxxxxxxxxx/#t > > > > And Jan's patch is almost identical to yours :) > > > > I hope to get this resolved, but I don't have time to work on it > > before the upcoming merge window, which will probably open Sunday. > > And then it's holiday time, so it may be January before I get back to > > it. I'm just dropping the links here as breadcrumbs for picking this > > back up. > > Thanks for the update! I was somewhat bemused by the dereference here, I’m > reassured to see I’m not the only one. Unfortunately I don’t have hardware > which exhibits this problem, Yeah, that's a weird thing about this. This shouldn't be a platform-specific thing, but both stackexchange and Jan's patch mention IBM x3850. Maybe both came from a single source, or maybe there's something deeper going on. > I submitted the patch because it seemed > reasonably sensible even though as you say there is probably something else > going on here. Of course if this approach is useful, Jan’s patch should go in > rather than mine. > > Anyway, it’s been six years, so a few more weeks won’t make any difference > ;-). > > Enjoy the holiday season! > > Regards, > > Stephen
