Hi Will, On 04/03/2013 02:04 PM, Will Deacon wrote: > Hi Christopher, > > On Wed, Apr 03, 2013 at 07:01:01PM +0100, Christopher Covington wrote: >> For accurate accounting call contextidr_thread_switch before a >> task is scheduled, rather than after. >> >> Signed-off-by: Christopher Covington <cov@xxxxxxxxxxxxxx> >> --- >> arch/arm64/kernel/process.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c >> index 0337cdb..c2cc249 100644 >> --- a/arch/arm64/kernel/process.c >> +++ b/arch/arm64/kernel/process.c >> @@ -311,11 +311,11 @@ struct task_struct *__switch_to(struct task_struct *prev, >> fpsimd_thread_switch(next); >> tls_thread_switch(next); >> hw_breakpoint_thread_switch(next); >> + contextidr_thread_switch(next); >> >> /* the actual thread switch */ >> last = cpu_switch_to(prev, next); >> >> - contextidr_thread_switch(next); >> return last; >> } > > Catalin and I wondered about this and decided to go with the current > approach in case a debugger, in response to the contextidr write, decided to > go off and mine information about the *new* task using the sp. The problem with the existing implementation is that it doesn't seem to compensate for how cpu_switch_to changes the stack pointer. Consider the following sequence. cpu_switch_to(prev=A, next=B) cpu_switch_to(prev=B, next=C) cpu_switch_to(prev=C, next=A) After the third call, using A's stack, next will be B, and its thread ID will be written to CONTEXTIDR. An easy way to see this in a simulator is to just instrument the code with some printk's. Thanks, Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
