uprobes: Do not play with utask in xol_get_insn_slot()

pre_ssout()->xol_get_insn_slot() path is confusing and buggy. This patch
cleanups the code, the next one fixes the bug.

Change xol_get_insn_slot() to only allocate the slot and do nothing more,
move the initialization of utask->xol_vaddr/vaddr into pre_ssout().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Anton Arapov <anton@redhat.com>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

1 files changed, 21 insertions, 16 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 16e54d63a9fd..8d9c5bcb110e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1176,30 +1176,26 @@ static unsigned long xol_take_insn_slot(struct xol_area *area)
 }
 
 /*
- * xol_get_insn_slot - If was not allocated a slot, then
- * allocate a slot.
+ * xol_get_insn_slot - allocate a slot for xol.
  * Returns the allocated slot address or 0.
  */
-static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot_addr)
+static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
 {
         struct xol_area *area;
         unsigned long offset;
+        unsigned long xol_vaddr;
         void *vaddr;
 
         area = get_xol_area();
         if (!area)
                 return 0;
 
-        current->utask->xol_vaddr = xol_take_insn_slot(area);
-        /*
-         * Initialize the slot if xol_vaddr points to valid
-         * instruction slot.
-         */
-        if (unlikely(!current->utask->xol_vaddr))
+        xol_vaddr = xol_take_insn_slot(area);
+        if (unlikely(!xol_vaddr))
                 return 0;
 
-        current->utask->vaddr = slot_addr;
-        offset = current->utask->xol_vaddr & ~PAGE_MASK;
+        /* Initialize the slot */
+        offset = xol_vaddr & ~PAGE_MASK;
         vaddr = kmap_atomic(area->page);
         memcpy(vaddr + offset, uprobe->arch.insn, MAX_UINSN_BYTES);
         kunmap_atomic(vaddr);
@@ -1209,7 +1205,7 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe, unsigned long slot
          */
         flush_dcache_page(area->page);
 
-        return current->utask->xol_vaddr;
+        return xol_vaddr;
 }
 
 /*
@@ -1306,12 +1302,21 @@ static struct uprobe_task *get_utask(void)
 
 /* Prepare to single-step probed instruction out of line. */
 static int
-pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long vaddr)
+pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
 {
-        if (xol_get_insn_slot(uprobe, vaddr) && !arch_uprobe_pre_xol(&uprobe->arch, regs))
-                return 0;
+        struct uprobe_task *utask;
+        unsigned long xol_vaddr;
+
+        utask = current->utask;
+
+        xol_vaddr = xol_get_insn_slot(uprobe);
+        if (!xol_vaddr)
+                return -ENOMEM;
+
+        utask->xol_vaddr = xol_vaddr;
+        utask->vaddr = bp_vaddr;
 
-        return -EFAULT;
+        return arch_uprobe_pre_xol(&uprobe->arch, regs);
 }
 
 /*