On Sun, Dec 05, 2021 at 07:46:39AM +0100, Thorsten Leemhuis wrote: > Hi, this is your Linux kernel regression tracker speaking. > > On 04.12.21 15:15, Hans de Goede wrote: > > Hi All, > > > > There are several bug reports (arch and Fedora) about USB problems > > starting with kernel 5.14.14 (5.14.13 is ok): > > > > https://bugzilla.redhat.com/show_bug.cgi?id=2019788 > > https://bbs.archlinux.org/viewtopic.php?pid=2006862 > > > > And 5.16.6, which has the hub address0_mutex fixes does not > > fix these problems for some users. > > > > Looking at the history between those 2 commit ff0e50d3564f > > ("xhci: Fix command ring pointer corruption while aborting a command"): > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ff0e50d3564f > > > > stood out to me as a possible cause of this. So I've build > > a test 5.15.6 kernel for Fedora users with that commit reverted > > and 2 users have now reported that this fixes things for them > > (see https://bugzilla.redhat.com/show_bug.cgi?id=2019788). > > > > The reason why this stood out to me is because doing a 32 bit > > write over a possibly 64 bit databus to the xHCI controller may > > result in the hw doing a 64 bit read + modify 32 bit + 64 bit write, > > so I think that the following is happening after the commit: > > > > sw: read 32 bit > > hw: read 64 bit, return 32 bit > > sw: modify it > > sw: write 32 bit > > hw: read 64 bit > > hw: modify 32 bit of 64 bit wor5d > > hw: write 64 bit > > > > Which actually makes the chances of hitting the problem the commit > > tries to fix larger on controllers using a 64 bit data bus. > > > > Note this is just a theory, but it seems plausible to me. > > > > All problem reports are people using integrated Intel xHCI controllers > > which I believe are likely to use a 64 bit data-bus. > > FWIW, the commit is known to cause problems, one of them is found here: > > https://lore.kernel.org/lkml/35f7428b39f996c793f5b4a6a314772681c73d7a.camel@xxxxxxxxxx/ > > This commit should improve the situation (and afaics hopefully fix all > problems related to it): > > https://lore.kernel.org/stable/20211126122340.1193239-2-mathias.nyman@xxxxxxxxxxxxxxx/ > > Greg wants to sent it upstream today: > > https://lore.kernel.org/lkml/YatGfEzzniH%2FSrn4@xxxxxxxxx/ > > Guess he soon after will backport it to the stable trees as well. > > HTH, Ciao, Thorsten > > #regzbot ^backmonitor > https://lore.kernel.org/lkml/35f7428b39f996c793f5b4a6a314772681c73d7a.camel@xxxxxxxxxx/ Ah, I should have read the whole thread, yes, this should be the fix for this. thanks, greg k-h
