Ananth N Mavinakayanahalli wrote: > On Mon, Jul 11, 2011 at 10:39:35AM +0800, Tiejun Chen wrote: >> When enable CONFIG_PREEMPT we will trigger the following call trace: >> >> BUG: scheduling while atomic: swapper/1/0x10000000 >> ... >> >> krpobe always goes through the following path: >> >> program_check_exception() >> | >> + notify_die(DIE_BPT, "breakpoint",...) >> | >> + kprobe_handler() >> | >> + preempt_disable(); >> + break_handler() <- preempt_enable_no_resched() >> + emulate_step() >> + preempt_enable_no_resched() >> ... >> exit >> >> We should remove unnecessary preempt_enable_no_resched() inside of >> break_handler() >> since looks longjmp_break_handler() always go the above path. > > The current code is correct. Reasoning follows... > > setjmp_pre_handler() and longjmp_break_handler() are used only for > jprobes. In the case of a jprobe, the code flow would be: > > bp hit -> kprobe_handler() -> preempt_disable() -> setjmp_pre_handler() > (not that since this routine returns 1, we skip sstep here) -> jp->entry() > -> jprobe_return() -> bp hit -> kprobe_handler() -> preempt_disable() again > -> longjmp_break_handler() -> preempt_enable() -> sstep -> preempt_enable() > (for the second kprobe_handler() entry). > > You could verify this with a preempt_count() printk with a > CONFIG_PREEMPT=y kernel. > >> Signed-off-by: Tiejun Chen <tiejun.c...@windriver.com> > > Nack, sorry :-)
You're right. When use EXC_LEVEL_EXCEPTION_PROLOG for Critical/Machine check, if the exception came from kernel mode, we copy thread_info flags, *preempt*, and task pointer from the process thread_info. So here I steal EXC_LEVEL_EXCEPTION_PROLOG for Program Exception, preempt count would be corrupted incorrectly. Thanks Tiejun > > Ananth > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev