On 11/13/2015 10:27 AM, Michael Neuling wrote: > Currently we can hit a scenario where we'll tm_reclaim() twice. This > results in a TM bad thing exception because the second reclaim occurs > when not in suspend mode. > > The scenario in which this can happen is the following. We attempt to > deliver a signal to userspace. To do this we need obtain the stack > pointer to write the signal context. To get this stack pointer we > must tm_reclaim() in case we need to use the checkpointed stack > pointer (see get_tm_stackpointer()). Normally we'd then return > directly to userspace to deliver the signal without going through > __switch_to(). > > Unfortunatley, if at this point we get an error (such as a bad > userspace stack pointer), we need to exit the process. The exit will > result in a __switch_to(). __switch_to() will attempt to save the > process state which results in another tm_reclaim(). This > tm_reclaim() now causes a TM Bad Thing exception as this state has > already been saved and the processor is no longer in TM suspend mode. > Whee! > > This patch checks the state of the MSR to ensure we are TM suspended > before we attempt the tm_reclaim(). If we've already saved the state > away, we should no longer be in TM suspend mode. This has the > additional advantage of checking for a potential TM Bad Thing > exception.
Can this situation be created using a test and verified that with this new change, the kernel can handle it successfully. I guess the self test in the series does not cover this scenario. > > Found using syscall fuzzer. > > Signed-off-by: Michael Neuling <mi...@neuling.org> > Cc: sta...@vger.kernel.org > --- > arch/powerpc/kernel/process.c | 19 +++++++++++++++++++ > 1 file changed, 19 insertions(+) > > diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c > index 5fbe5d8..a1b41d1 100644 > --- a/arch/powerpc/kernel/process.c > +++ b/arch/powerpc/kernel/process.c > @@ -551,6 +551,25 @@ static void tm_reclaim_thread(struct thread_struct *thr, > msr_diff &= MSR_FP | MSR_VEC | MSR_VSX | MSR_FE0 | MSR_FE1; > } > > + /* > + * Use the current MSR TM suspended bit to track if we have > + * checkpointed state outstanding. > + * On signal delivery, we'd normally reclaim the checkpointed > + * state to obtain stack pointer (see:get_tm_stackpointer()). > + * This will then directly return to userspace without going > + * through __switch_to(). However, if the stack frame is bad, > + * we need to exit this thread which calls __switch_to() which > + * will again attempt to reclaim the already saved tm state. > + * Hence we need to check that we've not already reclaimed > + * this state. > + * We do this using the current MSR, rather tracking it in > + * some specific bit thread_struct bit, as it has the There is one extra "bit" here ^^^^^. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
