Le 10/03/2021 à 02:22, Nicholas Piggin a écrit :

Excerpts from Christophe Leroy's message of March 9, 2021 10:09 pm:

quoted

unrecoverable_exception() is never expected to return, most callers
have an infiniteloop in case it returns.

Ensure it really never returns by terminating it with a BUG(), and
declare it __no_return.

It always GCC to really simplify functions calling it. In the exemple
below, it avoids the stack frame in the likely fast path and avoids
code duplication for the exit.

With this patch:

[snip]

Nice.

quoted

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index a44a30b0688c..d5c9d9ddd186 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c

@@ -2170,11 +2170,15 @@ DEFINE_INTERRUPT_HANDLER(SPEFloatingPointRoundException)
   * in the MSR is 0.  This indicates that SRR0/1 are live, and that
   * we therefore lost state by taking this exception.
   */
-void unrecoverable_exception(struct pt_regs *regs)
+void __noreturn unrecoverable_exception(struct pt_regs *regs)
  {
  	pr_emerg("Unrecoverable exception %lx at %lx (msr=%lx)\n",
  		 regs->trap, regs->nip, regs->msr);
  	die("Unrecoverable exception", regs, SIGABRT);
+	/* die() should not return */
+	WARN(true, "die() unexpectedly returned");
+	for (;;)
+		;
  }

I don't think the WARN should be added because that will cause another
interrupt after something is already badly wrong, so this might just
make it harder to debug.

For example if die() is falling through for some reason, we warn and
cause a program check here, and that might also be unrecoverable so it
might come through here and fall through again and warn again, etc.

Putting the infinite loop is good enough I think (and better than there
was previously).

Ok, dropped the WARN()

Otherwise

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

Thanks,
Nick