Hey Mikey, Thanks for the review.
On 08/15/2018 08:50 PM, Michael Neuling wrote: > On Mon, 2018-06-18 at 19:59 -0300, Breno Leitao wrote: >> If __switch_to() tries to context switch from task A to task B, and task A >> had task->thread->regs->msr[TM] enabled, then __switch_to_tm() will call >> tm_recheckpoint_new_task(), which will call trecheckpoint, for task B, which >> is clearly wrong since task B might not be an active TM user. >> >> This does not cause a lot of damage because tm_recheckpoint() will abort >> the call since it realize that the current task does not have msr[TM] bit >> set. >> >> Signed-off-by: Breno Leitao <lei...@debian.org> >> --- >> arch/powerpc/kernel/process.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c >> index f8beee03f00a..d26a150766ef 100644 >> --- a/arch/powerpc/kernel/process.c >> +++ b/arch/powerpc/kernel/process.c >> @@ -1036,7 +1036,8 @@ static inline void __switch_to_tm(struct task_struct >> *prev, >> prev->thread.regs->msr &= ~MSR_TM; >> } >> >> - tm_recheckpoint_new_task(new); >> + if (tm_enabled(new)) >> + tm_recheckpoint_new_task(new); > > I'm not sure we need this patch as tm_recheckpoint_new_task() does this > itself. My plan is to move this check prior to calling these TM functions, doing early checking and avoiding calling tm_recheckpoint on a non-tm enabled task. It is very weird when you see, during a tracing, a kernel thread (PF_KTHREAD) being tm_recheckpointed. :-/ That said, the TM function would do the operation other than "check and do it" mode. Ideally I would like to check the thread before calling any TM functions, and warning (WARN_ON) if we detect, later in the game, that a thread is not TM enabled. This helps on two different fronts, in my opinion: * Code readability * Understanding tracing (ftrace) outputs.
