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-rw-r--r--Documentation/powerpc/transactional_memory.txt32
-rw-r--r--arch/powerpc/include/uapi/asm/tm.h2
-rw-r--r--arch/powerpc/kernel/entry_64.S19
-rw-r--r--tools/testing/selftests/powerpc/tm/Makefile2
4 files changed, 18 insertions, 37 deletions
diff --git a/Documentation/powerpc/transactional_memory.txt b/Documentation/powerpc/transactional_memory.txt
index ba0a2a4..ded6979 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 5047659..5d836b7 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 8ca9434..afbc200 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 1b616fa..6bff955 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)
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