Re: [PATCH 07/14] powerpc: Add support for restartable sequences
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2018-05-24 01:03:39
Also in:
linuxppc-dev, lkml
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
Mathieu Desnoyers [off-list ref] writes:
----- On May 23, 2018, at 4:14 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:
...
quoted
Hi Boqun, I tried your patch in a ppc64 le environment, and it does not survive boot with CONFIG_DEBUG_RSEQ=y. init gets killed right away.
Sorry this code is super gross and hard to deal with.
quoted hunk ↗ jump to hunk
The following fixup gets ppc64 to work:--- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S@@ -208,6 +208,7 @@ system_call_exit: /* Check whether the syscall is issued inside a restartable sequence */ addi r3,r1,STACK_FRAME_OVERHEAD bl rseq_syscall + ld r3,RESULT(r1) #endif /* * Disable interrupts so current_thread_info()->flags can't change,
I don't think that's safe. If you look above that, we have r3, r8 and r12 all live: .Lsyscall_exit: std r3,RESULT(r1) CURRENT_THREAD_INFO(r12, r1) ld r8,_MSR(r1) #ifdef CONFIG_PPC_BOOK3S /* No MSR:RI on BookE */ andi. r10,r8,MSR_RI beq- .Lunrecov_restore #endif They're all volatile across function calls: http://openpowerfoundation.org/wp-content/uploads/resources/leabi/content/dbdoclet.50655240_68174.html The system_call_exit symbol is actually there for kprobes and cosmetic purposes. The actual syscall return flow starts at .Lsyscall_exit. So I think this would work:
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index db4df061c33a..e19f377a25e0 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S@@ -184,6 +184,14 @@ system_call: /* label this so stack traces look sane */ .Lsyscall_exit: std r3,RESULT(r1) + +#ifdef CONFIG_DEBUG_RSEQ + /* Check whether the syscall is issued inside a restartable sequence */ + addi r3,r1,STACK_FRAME_OVERHEAD + bl rseq_syscall + ld r3,RESULT(r1) +#endif + CURRENT_THREAD_INFO(r12, r1) ld r8,_MSR(r1)
I'll try and get this series into my test setup at some point, been a bit busy lately :) cheers