[PATCH 4/5] uprobes: teach set_xol_ip() to use uprobe_xol_slots[]

[Oleg Nesterov]

Change set_xol_ip() to use uprobe_xol_slots[] per-cpu array to
"allocate" the insn slot. We do not care if the task migrates to
another CPU before executing xol insn, set_xol_ip() will be called
again by uprobe_switch_to(). Likewise, we do not care if the task
is simply preempted or sleeps.

IOW, uprobe_xol_slots[CPU] is "owned" by cpu_curr(CPU).

This makes xol_get_insn_slot/xol_free_insn_slot unnecessary, but
uprobe_notify_resume() should set utask->vaddr. The patch updates
the callers but doesn't remove this code to simplify the review.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 kernel/uprobes.c |   16 ++++++++++------
 1 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 20007da..c9e2f65 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1285,7 +1285,6 @@ void free_uprobe_utask(struct task_struct *tsk)
 	if (utask->active_uprobe)
 		put_uprobe(utask->active_uprobe);
 
-	xol_free_insn_slot(tsk);
 	kfree(utask);
 	tsk->utask = NULL;
 }
@@ -1347,7 +1346,15 @@ uprobe_xol_slots[UPROBES_XOL_SLOT_BYTES][NR_CPUS] __page_aligned_bss;
 
 void __weak set_xol_ip(struct pt_regs *regs)
 {
-	set_instruction_pointer(regs, current->utask->xol_vaddr);
+	int cpu = smp_processor_id();
+	struct uprobe_task *utask = current->utask;
+	struct uprobe *uprobe = utask->active_uprobe;
+
+	memcpy(uprobe_xol_slots[cpu], uprobe->insn, MAX_UINSN_BYTES);
+
+	utask->xol_vaddr = fix_to_virt(UPROBE_XOL_FIRST_PAGE)
+				+ UPROBES_XOL_SLOT_BYTES * cpu;
+	set_instruction_pointer(regs, utask->xol_vaddr);
 }
 
 /*
@@ -1390,14 +1397,12 @@ void uprobe_notify_resume(struct pt_regs *regs)
 				goto cleanup_ret;
 		}
 		utask->active_uprobe = u;
+		utask->vaddr = probept;
 		handler_chain(u, regs);
 
 		if (u->flags & UPROBES_SKIP_SSTEP && can_skip_xol(regs, u))
 			goto cleanup_ret;
 
-		if (!xol_get_insn_slot(u, probept))
-			goto cleanup_ret;
-
 		if (pre_xol(u, regs))
 			goto cleanup_ret;
 
@@ -1419,7 +1424,6 @@ void uprobe_notify_resume(struct pt_regs *regs)
 		utask->active_uprobe = NULL;
 		utask->state = UTASK_RUNNING;
 		user_disable_single_step(current);
-		xol_free_insn_slot(current);
 
 		spin_lock_irq(&current->sighand->siglock);
 		recalc_sigpending(); /* see uprobe_deny_signal() */
-- 
1.5.5.1


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