| Message ID | 1365012061-31660-1-git-send-email-cov@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@codeaurora.org> >> --- >> 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
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@codeaurora.org> > >> --- > >> 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
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; }
For accurate accounting call contextidr_thread_switch before a task is scheduled, rather than after. Signed-off-by: Christopher Covington <cov@codeaurora.org> --- arch/arm64/kernel/process.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)