Messages in this thread | | | Date | Mon, 18 Aug 2008 22:28:31 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: ftrace introduces instability into kernel 2.6.27(-rc2,-rc3) |
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On Tue, 19 Aug 2008, Benjamin Herrenschmidt wrote:
> On Mon, 2008-08-18 at 14:27 -0400, Steven Rostedt wrote: > > > > On Mon, 18 Aug 2008, Scott Wood wrote: > > > > > Mathieu Desnoyers wrote: > > > > asm volatile ( > > > > "1: lwz %1, 0(%2)\n" > > > > " cmpw %1, %5\n" > > > > " bne 2f\n" > > > > " stwu %3, 0(%2)\n" > > > > "2:\n" > > > > ".section .fixup, \"ax\"\n" > > > > "3: li %0, 1\n" > > > > " b 2b\n" > > > > ".previous\n" > > > > ".section __ex_table,\"a\"\n" > > > > _ASM_ALIGN "\n" > > > > _ASM_PTR "1b, 3b\n" > > > > ".previous" > > > > : "=r"(faulted), "=r"(replaced) > > > > : "r"(ip), "r"(new), > > > > "0"(faulted), "r"(old) > > > > : "memory"); > > > > > > Some (most likely unrelated) nits in the above inline asm: > > > Why not use __get_user/__put_user ?
Hmm, this was originally copied from x86, where we did a cmpxchg, but that is probably not needed since all of this is done in kstop_machine. Also, only the "get" is needed. If we don't fault there, we wont fault on the put (unless we have permissions wrong, and that would be a bug).
So are you recommending something like
int cmd;
if (__get_user(cmd, ip)) goto fault;
if (cmd != old) goto not_same;
WARN_ON_ONCE(__put_user(cmd, ip));
If we did this, we could probably put this into the generic code:
if (copy_from_user(cmd, ip, ARCH_CALL_SIZE)) goto fault;
if (memcmp(cmd, old, ARCH_CALL_SIZE) != 0) goto not_same;
WARN_ON_ONCE(copy_to_user(cmd, ip, ARCH_CALL_SIZE));
-- Steve
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