On Mon, Apr 08, 2013 at 03:42:24PM +0100, Christopher Covington wrote: > 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. Yes, but moving the call still isn't the right thing to do if we can avoid it. How about making that contextidr_thread_switch take prev instead of next? Will -- 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
