On Wed, Jul 26, 2017 at 5:02 AM, Will Deacon <will.dea...@arm.com> wrote: > On Tue, Jul 25, 2017 at 01:01:17PM -0700, Thomas Garnier wrote: >> On Tue, Jul 25, 2017 at 3:38 AM, Russell King - ARM Linux >> <li...@armlinux.org.uk> wrote: >> > On Tue, Jul 25, 2017 at 01:28:01PM +0300, Leonard Crestez wrote: >> >> On Mon, 2017-07-24 at 10:07 -0700, Thomas Garnier wrote: >> >> > On Wed, Jul 19, 2017 at 10:58 AM, Thomas Garnier <thgar...@google.com >> >> > > wrote: >> >> > > >> >> > > The work pending loop can call set_fs after addr_limit_user_check >> >> > > removed the _TIF_FSCHECK flag. To prevent the infinite loop, move >> >> > > the addr_limit_user_check call at the beginning of the loop. >> >> > > >> >> > > Fixes: 73ac5d6a2b6a ("arm/syscalls: Check address limit on user- >> >> > > mode return") >> >> > > Reported-by: Leonard Crestez <leonard.cres...@nxp.com> >> >> > > Signed-off-by: Thomas Garnier <thgar...@google.com> >> >> >> >> > Any comments on this patch set? >> >> >> >> Tested-by: Leonard Crestez <leonard.cres...@nxp.com> >> >> >> >> This appears to fix the original issue of failing to boot from NFS when >> >> there are lots of alignment faults. But this is a very basic test >> >> relative to the reach of this change. >> >> >> >> However the original patch has been in linux-next for a while and >> >> apparently nobody else noticed system calls randomly hanging on arm. >> >> >> >> I assume maintainers need to give their opinion. >> > >> > I've already stated my opinion, which is different from what Linus has >> > requested of Thomas. IMHO, the current approach is going to keep on >> > causing problems along the lines that I've already pointed out. >> >> I understand. Do you think this problem apply to arm64 as well? > > It's probably less of an issue for arm64 because we don't take alignment > faults from the kernel and I think the perf case would resolve itself by > throttling the event. However, I also don't see the advantage of doing > this in the work loop as opposed to leaving it until we're actually doing > the return to userspace.
I think the idea is doing the check as early as possible to catch any error before any additional logic. > > I looked to see what you've done for x86, but it looks like you check/clear > the flag before the work pending loop (exit_to_usermode_loop), which > subsequently re-enables interrupts and exits when > EXIT_TO_USERMODE_LOOP_FLAGS are all clear. Since TIF_FSCHECK isn't included > in those flags, what stops it being set again by an irq and remaining set > for the return to userspace? Nothing, I plan to improve the x86 logic later. I focused on ARM/ARM64 right now based on Leonard report. For the next iteration, I plan on having an updated version of the previous implementation for ARM. I will send it soon. > > Will -- Thomas