diff options
| author | Ravi Bangoria | 2016-03-02 15:25:17 +0530 |
|---|---|---|
| committer | Michael Ellerman | 2016-03-03 22:06:08 +1100 |
| commit | fb822e6076d972691c5dd33431c10f82dda94ae9 (patch) | |
| tree | 95aefc3d511923fdb5438166bbb4d7e70cddfa85 /arch | |
| parent | 923adb1646d5ba739d2a1e63ee20d60574d9da8e (diff) | |
powerpc/hw_breakpoint: Fix oops when destroying hw_breakpoint event
When destroying a hw_breakpoint event, the kernel oopses as follows:
Unable to handle kernel paging request for data at address 0x00000c07
NIP [c0000000000291d0] arch_unregister_hw_breakpoint+0x40/0x60
LR [c00000000020b6b4] release_bp_slot+0x44/0x80
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.
Peterz points out that the code shouldn't be using bp->ctx anyway, but
fixing that will require a decent amount of rework. So for now to fix
the oops, check if bp->ctx->task has been set to (void *)-1, before
dereferencing it. We don't use TASK_TOMBSTONE, because that would
require exporting it and it's supposed to be an internal detail.
Fixes: 63b6da39bb38 ("perf: Fix perf_event_exit_task() race")
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/powerpc/kernel/hw_breakpoint.c | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c index 05e804cdecaa..aec9a1b1d25b 100644 --- a/arch/powerpc/kernel/hw_breakpoint.c +++ b/arch/powerpc/kernel/hw_breakpoint.c @@ -109,8 +109,9 @@ void arch_unregister_hw_breakpoint(struct perf_event *bp) * If the breakpoint is unregistered between a hw_breakpoint_handler() * and the single_step_dabr_instruction(), then cleanup the breakpoint * restoration variables to prevent dangling pointers. + * FIXME, this should not be using bp->ctx at all! Sayeth peterz. */ - if (bp->ctx && bp->ctx->task) + if (bp->ctx && bp->ctx->task && bp->ctx->task != ((void *)-1L)) bp->ctx->task->thread.last_hit_ubp = NULL; } |