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authorOleg Nesterov <oleg@redhat.com>2013-07-09 01:00:58 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-09 19:33:26 +0200
commit29a55513414187b50d3cebb99884955a78d97283 (patch)
treeb02319f6fbfeae97165ba7fcf606b5ef7791d73b
parentptrace/x86: simplify the "disable" logic in ptrace_write_dr7() (diff)
downloadlinux-29a55513414187b50d3cebb99884955a78d97283.tar.xz
linux-29a55513414187b50d3cebb99884955a78d97283.zip
ptrace/x86: dont delay "disable" till second pass in ptrace_write_dr7()
ptrace_write_dr7() skips ptrace_modify_breakpoint(disabled => true) unless second_pass, this buys nothing but complicates the code and means that we always do the main loop twice even if "disabled" was never true. The comment says: Don't unregister the breakpoints right-away, unless all register_user_hw_breakpoint() requests have succeeded. Firstly, we do not do register_user_hw_breakpoint(), it was removed by commit 24f1e32c60c4 ("hw-breakpoints: Rewrite the hw-breakpoints layer on top of perf events"). We are going to restore register_user_hw_breakpoint() (see the next patch) but this doesn't matter: after commit 44234adcdce3 ("hw-breakpoints: Modify breakpoints without unregistering them") perf_event_disable() can not hurt, hw_breakpoint_del() does not free the slot. Remove the "second_pass" check from the main loop and simplify the code. Since we have to check "bp != NULL" anyway, the patch also removes the same check in ptrace_modify_breakpoint() and moves the comment into ptrace_write_dr7(). With this patch the second pass is only needed to restore the saved old_dr7. This should never fail, so the patch adds WARN_ON() to catch the potential problems as Frederic suggested. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: Jan Kratochvil <jan.kratochvil@redhat.com> Cc: Michael Neuling <mikey@neuling.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Paul Mundt <lethal@linux-sh.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Prasad <prasad@linux.vnet.ibm.com> Cc: Russell King <linux@arm.linux.org.uk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--arch/x86/kernel/ptrace.c53
1 files changed, 20 insertions, 33 deletions
diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
index 0649f166d7c6..98b0a2ccc33c 100644
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -609,14 +609,6 @@ ptrace_modify_breakpoint(struct perf_event *bp, int len, int type,
int gen_len, gen_type;
struct perf_event_attr attr;
- /*
- * We should have at least an inactive breakpoint at this
- * slot. It means the user is writing dr7 without having
- * written the address register first
- */
- if (!bp)
- return -EINVAL;
-
err = arch_bp_generic_fields(len, type, &gen_len, &gen_type);
if (err)
return err;
@@ -634,52 +626,47 @@ ptrace_modify_breakpoint(struct perf_event *bp, int len, int type,
*/
static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data)
{
- struct thread_struct *thread = &(tsk->thread);
+ struct thread_struct *thread = &tsk->thread;
unsigned long old_dr7;
- int i, orig_ret = 0, rc = 0;
- int second_pass = 0;
+ bool second_pass = false;
+ int i, rc, ret = 0;
data &= ~DR_CONTROL_RESERVED;
old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
+
restore:
- /*
- * Loop through all the hardware breakpoints, making the
- * appropriate changes to each.
- */
+ rc = 0;
for (i = 0; i < HBP_NUM; i++) {
unsigned len, type;
bool disabled = !decode_dr7(data, i, &len, &type);
struct perf_event *bp = thread->ptrace_bps[i];
- if (disabled) {
+ if (!bp) {
+ if (disabled)
+ continue;
/*
- * Don't unregister the breakpoints right-away, unless
- * all register_user_hw_breakpoint() requests have
- * succeeded. This prevents any window of opportunity
- * for debug register grabbing by other users.
+ * We should have at least an inactive breakpoint at
+ * this slot. It means the user is writing dr7 without
+ * having written the address register first.
*/
- if (!bp || !second_pass)
- continue;
+ rc = -EINVAL;
+ break;
}
rc = ptrace_modify_breakpoint(bp, len, type, tsk, disabled);
if (rc)
break;
}
- /*
- * Make a second pass to free the remaining unused breakpoints
- * or to restore the original breakpoints if an error occurred.
- */
- if (!second_pass) {
- second_pass = 1;
- if (rc < 0) {
- orig_ret = rc;
- data = old_dr7;
- }
+
+ /* Restore if the first pass failed, second_pass shouldn't fail. */
+ if (rc && !WARN_ON(second_pass)) {
+ ret = rc;
+ data = old_dr7;
+ second_pass = true;
goto restore;
}
- return orig_ret < 0 ? orig_ret : rc;
+ return ret;
}
/*