Hi Dave:
Coming back to the perf userspace callchain problem. As a reminder there are
a series of problems trying to use perf to collect callchains with scheduling
tracepoints, e.g., perf sched record -g -- <cmd>.
The first patch disables pagefaults while walking the user stack. As discussed
a couple of months ago this is the right fix, but I was puzzled as to why
processes were terminating with sigbus (and sometimes sigsegv). I believe the
root of this problem is bad addresses trying to walk the frames using frame
pointers. The bad addresses lead to faults that get handled by do_sparc64_fault
and it aborts the task though I am still puzzled as to why it gets past this
check in do_sparc64_fault:
if (in_atomic() || !mm)
goto intr_or_no_mm;
pagefault_disable bumps the preempt_count which should make in_atomic return != 0
(building kernels with preemption set to voluntar, CONFIG_PREEMPT_VOLUNTARY=y).
While this set does not fully solve the problem it does prevent a number of
pain points with the current code, most notably able to lock up the system.
David Ahern (4):
sparc: perf: Disable pagefaults while walking userspace stacks
sparc64: Convert BUG_ON to warning
sparc64: perf: Add sanity checking on addresses in user stack
sparc64: perf: Use UREG_FP rather than UREG_I6
arch/sparc/include/asm/uaccess_64.h | 22 ++++++++++++++++++++++
arch/sparc/kernel/perf_event.c | 24 +++++++++++++++++++++---
arch/sparc/mm/fault_64.c | 5 +++--
3 files changed, 46 insertions(+), 5 deletions(-)
--
2.3.0
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