On Wed, Jul 26, 2017 at 11:25 AM, Russell King - ARM Linux <[email protected]> wrote: > On Wed, Jul 26, 2017 at 07:20:22AM -0700, Thomas Garnier wrote: >> On Wed, Jul 26, 2017 at 5:02 AM, Will Deacon <[email protected]> wrote: >> > 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. > > Hmm. In this case, I'd suggest concentrating on x86 and getting the > implementation correct there before porting it to other architectures.
I think the ARM architecture is different. > > If x86 were to check TIF_FSCHECK in the loop, and repeat until clear, > would x86 also end up in these infinite loops that have been reported > on ARM as well? If for every loop set_fs was called. I think the idea is that at some point only the TIF_FSCHECK remain. I don't think x86 suffers from the same issue than ARM. > > I strongly suggest testing the behaviour with kprobes/tracing enabled > for a function called from the work pending loop, and checking how > that behaves. > > -- > RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up > according to speedtest.net. -- Thomas
