On Wed, Mar 02, 2016 at 03:25:17PM +0530, Ravi Bangoria wrote: > At a time of destroying hw_breakpoint event, kernel ends up with Oops. > Here is the sample output from 4.5.0-rc6 kernel.
> Call chain: > > hw_breakpoint_event_init() > bp->destroy = bp_perf_event_destroy; > > do_exit() > perf_event_exit_task() > perf_event_exit_task_context() > WRITE_ONCE(child_ctx->task, TASK_TOMBSTONE); > perf_event_exit_event() > free_event() > _free_event() > bp_perf_event_destroy()//event->destroy(event); > release_bp_slot() > arch_unregister_hw_breakpoint() > > perf_event_exit_task_context sets child_ctx->task as TASK_TOMBSTONE > which is (void *)-1. arch_unregister_hw_breakpoint tries to fetch > 'thread' attribute of 'task' resulting in Oops. > > This patch adds one more condition before accessing data from 'task'. > > Signed-off-by: Ravi Bangoria <ravi.bango...@linux.vnet.ibm.com> > --- > arch/powerpc/kernel/hw_breakpoint.c | 3 ++- > include/linux/perf_event.h | 2 ++ > kernel/events/core.c | 2 -- > 3 files changed, 4 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/kernel/hw_breakpoint.c > b/arch/powerpc/kernel/hw_breakpoint.c > index 05e804c..43d8496 100644 > --- a/arch/powerpc/kernel/hw_breakpoint.c > +++ b/arch/powerpc/kernel/hw_breakpoint.c > @@ -29,6 +29,7 @@ > #include <linux/kernel.h> > #include <linux/sched.h> > #include <linux/smp.h> > +#include <linux/perf_event.h> > > #include <asm/hw_breakpoint.h> > #include <asm/processor.h> > @@ -110,7 +111,7 @@ void arch_unregister_hw_breakpoint(struct perf_event *bp) > * and the single_step_dabr_instruction(), then cleanup the breakpoint > * restoration variables to prevent dangling pointers. > */ > - if (bp->ctx && bp->ctx->task) > + if (bp->ctx && bp->ctx->task && bp->ctx->task != TASK_TOMBSTONE) > bp->ctx->task->thread.last_hit_ubp = NULL; > } Yuck.. you should not be touching ctx (esp not this late). And I suppose you cannot use bp->hw.target either because we don't actually keep that up-to-date. Why do you keep per task state anyway? What do per-cpu breakpoints do? _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev