tree 1260122ddfe4ae26ad224367097e2ca38fc8c6be
parent 771e569e8200ab6f5cdbcd6513f7a476718bb44d
author Sam bobroff <sam.bobroff@au1.ibm.com> 1428639407 +1000
committer Michael Ellerman <mpe@ellerman.id.au> 1428749359 +1000

powerpc/tm: Abort syscalls in active transactions

This patch changes the syscall handler to doom (tabort) active
transactions when a syscall is made and return immediately without
performing the syscall.

Currently, the system call instruction automatically suspends an
active transaction which causes side effects to persist when an active
transaction fails.

This does change the kernel's behaviour, but in a way that was
documented as unsupported. It doesn't reduce functionality because
syscalls will still be performed after tsuspend. It also provides a
consistent interface and makes the behaviour of user code
substantially the same across powerpc and platforms that do not
support suspended transactions (e.g. x86 and s390).

Performance measurements using
http://ozlabs.org/~anton/junkcode/null_syscall.c
indicate the cost of a system call increases by about 0.5%.

Signed-off-by: Sam Bobroff <sam.bobroff@au1.ibm.com>
Acked-By: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>