diff options
| -rw-r--r-- | Documentation/powerpc/transactional_memory.txt | 32 | ||||
| -rw-r--r-- | arch/powerpc/include/uapi/asm/tm.h | 2 | ||||
| -rw-r--r-- | arch/powerpc/kernel/entry_64.S | 19 | ||||
| -rw-r--r-- | tools/testing/selftests/powerpc/tm/Makefile | 2 |
4 files changed, 18 insertions, 37 deletions
diff --git a/Documentation/powerpc/transactional_memory.txt b/Documentation/powerpc/transactional_memory.txt index ba0a2a4a54ba..ded69794a5c0 100644 --- a/Documentation/powerpc/transactional_memory.txt +++ b/Documentation/powerpc/transactional_memory.txt @@ -74,23 +74,22 @@ Causes of transaction aborts Syscalls ======== -Syscalls made from within an active transaction will not be performed and the -transaction will be doomed by the kernel with the failure code TM_CAUSE_SYSCALL -| TM_CAUSE_PERSISTENT. +Performing syscalls from within transaction is not recommended, and can lead +to unpredictable results. -Syscalls made from within a suspended transaction are performed as normal and -the transaction is not explicitly doomed by the kernel. However, what the -kernel does to perform the syscall may result in the transaction being doomed -by the hardware. The syscall is performed in suspended mode so any side -effects will be persistent, independent of transaction success or failure. No -guarantees are provided by the kernel about which syscalls will affect -transaction success. +Syscalls do not by design abort transactions, but beware: The kernel code will +not be running in transactional state. The effect of syscalls will always +remain visible, but depending on the call they may abort your transaction as a +side-effect, read soon-to-be-aborted transactional data that should not remain +invisible, etc. If you constantly retry a transaction that constantly aborts +itself by calling a syscall, you'll have a livelock & make no progress. -Care must be taken when relying on syscalls to abort during active transactions -if the calls are made via a library. Libraries may cache values (which may -give the appearance of success) or perform operations that cause transaction -failure before entering the kernel (which may produce different failure codes). -Examples are glibc's getpid() and lazy symbol resolution. +Simple syscalls (e.g. sigprocmask()) "could" be OK. Even things like write() +from, say, printf() should be OK as long as the kernel does not access any +memory that was accessed transactionally. + +Consider any syscalls that happen to work as debug-only -- not recommended for +production use. Best to queue them up till after the transaction is over. Signals @@ -177,7 +176,8 @@ kernel aborted a transaction: TM_CAUSE_RESCHED Thread was rescheduled. TM_CAUSE_TLBI Software TLB invalid. TM_CAUSE_FAC_UNAV FP/VEC/VSX unavailable trap. - TM_CAUSE_SYSCALL Syscall from active transaction. + TM_CAUSE_SYSCALL Currently unused; future syscalls that must abort + transactions for consistency will use this. TM_CAUSE_SIGNAL Signal delivered. TM_CAUSE_MISC Currently unused. TM_CAUSE_ALIGNMENT Alignment fault. diff --git a/arch/powerpc/include/uapi/asm/tm.h b/arch/powerpc/include/uapi/asm/tm.h index 5047659815a5..5d836b7c1176 100644 --- a/arch/powerpc/include/uapi/asm/tm.h +++ b/arch/powerpc/include/uapi/asm/tm.h @@ -11,7 +11,7 @@ #define TM_CAUSE_RESCHED 0xde #define TM_CAUSE_TLBI 0xdc #define TM_CAUSE_FAC_UNAV 0xda -#define TM_CAUSE_SYSCALL 0xd8 +#define TM_CAUSE_SYSCALL 0xd8 /* future use */ #define TM_CAUSE_MISC 0xd6 /* future use */ #define TM_CAUSE_SIGNAL 0xd4 #define TM_CAUSE_ALIGNMENT 0xd2 diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S index 8ca9434c40e6..afbc20019c2e 100644 --- a/arch/powerpc/kernel/entry_64.S +++ b/arch/powerpc/kernel/entry_64.S @@ -34,7 +34,6 @@ #include <asm/ftrace.h> #include <asm/hw_irq.h> #include <asm/context_tracking.h> -#include <asm/tm.h> /* * System calls. @@ -146,24 +145,6 @@ END_FW_FTR_SECTION_IFSET(FW_FEATURE_SPLPAR) andi. r11,r10,_TIF_SYSCALL_DOTRACE bne syscall_dotrace .Lsyscall_dotrace_cont: -#ifdef CONFIG_PPC_TRANSACTIONAL_MEM -BEGIN_FTR_SECTION - b 1f -END_FTR_SECTION_IFCLR(CPU_FTR_TM) - extrdi. r11, r12, 1, (63-MSR_TS_T_LG) /* transaction active? */ - beq+ 1f - - /* Doom the transaction and don't perform the syscall: */ - mfmsr r11 - li r12, 1 - rldimi r11, r12, MSR_TM_LG, 63-MSR_TM_LG - mtmsrd r11, 0 - li r11, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT) - TABORT(R11) - - b .Lsyscall_exit -1: -#endif cmpldi 0,r0,NR_syscalls bge- syscall_enosys diff --git a/tools/testing/selftests/powerpc/tm/Makefile b/tools/testing/selftests/powerpc/tm/Makefile index 1b616fa79e93..6bff955e1d55 100644 --- a/tools/testing/selftests/powerpc/tm/Makefile +++ b/tools/testing/selftests/powerpc/tm/Makefile @@ -1,4 +1,4 @@ -TEST_PROGS := tm-resched-dscr tm-syscall +TEST_PROGS := tm-resched-dscr all: $(TEST_PROGS) |