linux-kernel - [PATCH 7/X] uprobes: xol_add_vma: simply use TASK

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Date:	Sun, 16 Oct 2011 18:18:27 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linux-mm <linux-mm@...ck.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Hugh Dickins <hughd@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	Roland McGrath <roland@...k.frob.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH 7/X] uprobes: xol_add_vma: simply use TASK_SIZE as a hint

I don't understand why xol_add_vma() abuses mm->mm_rb to find the
highest mapping. We can simply use TASK_SIZE-PAGE_SIZE a hint.

If this area is already occupied, the hint will be ignored with
or without this change. Otherwise the result is "obviously better"
and the code becomes simpler.

---

 kernel/uprobes.c |   13 ++++---------
 1 files changed, 4 insertions(+), 9 deletions(-)

diff --git a/kernel/uprobes.c b/kernel/uprobes.c
index 038f21c..b876977 100644
--- a/kernel/uprobes.c
+++ b/kernel/uprobes.c
@@ -1045,9 +1045,7 @@ void munmap_uprobe(struct vm_area_struct *vma)
 /* Slot allocation for XOL */
 static int xol_add_vma(struct uprobes_xol_area *area)
 {
-	struct vm_area_struct *vma;
 	struct mm_struct *mm;
-	unsigned long addr_hint;
 	int ret;
 
 	area->page = alloc_page(GFP_HIGHUSER);
@@ -1060,15 +1058,12 @@ static int xol_add_vma(struct uprobes_xol_area *area)
 	ret = -EALREADY;
 	if (mm->uprobes_xol_area)
 		goto fail;
+
 	/*
-	 * Find the end of the top mapping and skip a page.
-	 * If there is no space for PAGE_SIZE above that,
-	 * this hint will be ignored.
+	 * Try to map as high as possible, this is only a hint.
 	 */
-	vma = rb_entry(rb_last(&mm->mm_rb), struct vm_area_struct, vm_rb);
-	addr_hint = vma->vm_end + PAGE_SIZE;
-
-	area->vaddr = get_unmapped_area(NULL, addr_hint, PAGE_SIZE, 0, 0);
+	area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE,
+					PAGE_SIZE, 0, 0);
 	if (IS_ERR_VALUE(area->vaddr)) {
 		ret = area->vaddr;
 		goto fail;

--
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