path: root/Documentation
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authorLinus Torvalds <>2015-05-03 10:28:36 -0700
committerLinus Torvalds <>2015-05-03 10:28:36 -0700
commit180d89f6ef9c22d088e324eb5e7d030ef3f84df0 (patch)
treee9e9a4f24f8d056eed34c89bfe3209f33c189b7e /Documentation
parent6c3c1eb3c35e8856d6dcb01b412316a676f58bbe (diff)
parent0aab3747091db309b8a484cfd382a41644552aa3 (diff)
Merge tag 'powerpc-4.1-3' of git://
Pull powerpc fixes from Michael Ellerman: - build fix for SMP=n in book3s_xics.c - fix for Daniel's pci_controller_ops on powernv. - revert the TM syscall abort patch for now. - CPU affinity fix from Nathan. - two EEH fixes from Gavin. - fix for CR corruption from Sam. - selftest build fix. * tag 'powerpc-4.1-3' of git:// powerpc/powernv: Restore non-volatile CRs after nap powerpc/eeh: Delay probing EEH device during hotplug powerpc/eeh: Fix race condition in pcibios_set_pcie_reset_state() powerpc/pseries: Correct cpu affinity for dlpar added cpus selftests/powerpc: Fix the pmu install rule Revert "powerpc/tm: Abort syscalls in active transactions" powerpc/powernv: Fix early pci_controller_ops loading. powerpc/kvm: Fix SMP=n build error in book3s_xics.c
Diffstat (limited to 'Documentation')
1 files changed, 16 insertions, 16 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 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
+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.
@@ -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.