ptrace/x86: revert "hw_breakpoints: Fix racy access to ptrace breakpoints"

This reverts commit 87dc669ba257 ("hw_breakpoints: Fix racy access to
ptrace breakpoints").

The patch was fine but we can no longer race with SIGKILL after commit
9899d11f6544 ("ptrace: ensure arch_ptrace/ptrace_request can never race
with SIGKILL"), the __TASK_TRACED tracee can't be woken up and
->ptrace_bps[] can't go away.

The patch only removes ptrace_get_breakpoints/ptrace_put_breakpoints and
does a couple of "while at it" cleanups, it doesn't remove other changes
from the reverted commit.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.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>

arch/x86/kernel/ptrace.c

@@ -641,9 +641,6 @@ static int ptrace_write_dr7(struct task_struct *tsk, unsigned long data)
 	unsigned len, type;
 	struct perf_event *bp;
 
-	if (ptrace_get_breakpoints(tsk) < 0)
-		return -ESRCH;
-
 	data &= ~DR_CONTROL_RESERVED;
 	old_dr7 = ptrace_get_dr7(thread->ptrace_bps);
 restore:
@@ -692,9 +689,7 @@ restore:
 		goto restore;
 	}
 
-	ptrace_put_breakpoints(tsk);
-
-	return ((orig_ret < 0) ? orig_ret : rc);
+	return orig_ret < 0 ? orig_ret : rc;
 }
 
 /*
@@ -706,18 +701,10 @@ static unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
 	unsigned long val = 0;
 
 	if (n < HBP_NUM) {
-		struct perf_event *bp;
+		struct perf_event *bp = thread->ptrace_bps[n];
 
-		if (ptrace_get_breakpoints(tsk) < 0)
-			return -ESRCH;
-
-		bp = thread->ptrace_bps[n];
-		if (!bp)
-			val = 0;
-		else
+		if (bp)
 			val = bp->hw.info.address;
-
-		ptrace_put_breakpoints(tsk);
 	} else if (n == 6) {
 		val = thread->debugreg6;
 	 } else if (n == 7) {
@@ -734,9 +721,6 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
 	struct perf_event_attr attr;
 	int err = 0;
 
-	if (ptrace_get_breakpoints(tsk) < 0)
-		return -ESRCH;
-
 	if (!t->ptrace_bps[nr]) {
 		ptrace_breakpoint_init(&attr);
 		/*
@@ -762,7 +746,7 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
 		 */
 		if (IS_ERR(bp)) {
 			err = PTR_ERR(bp);
-			goto put;
+			goto out;
 		}
 
 		t->ptrace_bps[nr] = bp;
@@ -773,9 +757,7 @@ static int ptrace_set_breakpoint_addr(struct task_struct *tsk, int nr,
 		attr.bp_addr = addr;
 		err = modify_user_hw_breakpoint(bp, &attr);
 	}
-
-put:
-	ptrace_put_breakpoints(tsk);
+out:
 	return err;
 }