On Mon, Jul 20, 2015 at 7:20 AM, Guenter Roeck <[email protected]> wrote: > On Mon, Jul 20, 2015 at 11:53:45AM +0100, Will Deacon wrote: >> On Mon, Jul 20, 2015 at 08:36:47AM +0100, Ingo Molnar wrote: >> > * Olof Johansson <[email protected]> wrote: >> > >> > > Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'") >> > > moved the thread_struct to the bottom of task_struct. As a result, the >> > > offset is now too large to be used in an immediate add on arm64 with >> > > some kernel configs: >> > > >> > > arch/arm64/kernel/entry.S: Assembler messages: >> > > arch/arm64/kernel/entry.S:588: Error: immediate out of range >> > > arch/arm64/kernel/entry.S:597: Error: immediate out of range >> > > >> > > There's really no reason for cpu_switch_to to take a task_struct pointer >> > > in the first place, since all it does is access the thread.cpu_context >> > > member. So, just pass that in directly. >> > > >> > > Fixes: 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'") >> > > Cc: Dave Hansen <[email protected]> >> > > Signed-off-by: Olof Johansson <[email protected]> >> > > --- >> > > arch/arm64/include/asm/processor.h | 4 ++-- >> > > arch/arm64/kernel/asm-offsets.c | 2 -- >> > > arch/arm64/kernel/entry.S | 34 >> > > ++++++++++++++++------------------ >> > > arch/arm64/kernel/process.c | 3 ++- >> > > 4 files changed, 20 insertions(+), 23 deletions(-) >> > >> > So why not pass in 'thread_struct' as the patch below does - it looks much >> > simpler to me. This way the assembly doesn't have to be changed at all. >> >> Unfortunately, neither of these approaches really work: >> >> - We need to return last from __switch_to, which means not corrupting >> x0 in cpu_switch_to and then having an ugly container_of to get back >> at the task_struct >> >> - ret_from_fork needs to pass the task_struct of prev to schedule_tail, >> so we have the same issue there >> > Confirmed; both Ingo's patch (after fixing it up) and Olof's patch > fail my qemu tests (qemu hangs with both patches and does not produce > any console output). > >> Patch below fixes things, but it's a shame we have to use an extra register >> like this. >> > Yes, your patch works, at least with my qemu tests, and the allmodconfig build > no longer fails. > > Tested-by: Guenter Roeck <[email protected]>
Yep, my bad for not looking harder (and resurrecting my only arm64 test system that's currently down). Thanks all. :) -Olof -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
