linux-kernel - [PATCHv2 01/12] uprobes: split THPs before trying replace them

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Date:   Wed, 25 Jan 2017 21:25:27 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Andrea Arcangeli <aarcange@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCHv2 01/12] uprobes: split THPs before trying replace them

For THPs page_check_address() always fails. It leads to endless loop in
uprobe_write_opcode().

Testcase with huge-tmpfs (not sure if it's possible to trigger this
uprobe codepath for anon memory):

	mount -t debugfs none /sys/kernel/debug
	mount -t tmpfs -o huge=always none /mnt
	gcc -Wall -O2 -o /mnt/test -x c - <<EOF
	int main(void)
	{
		return 0;
	}
	/* Padding to map the code segment with huge pmd */
	asm (".zero 2097152");
	EOF
	echo 'p /mnt/test:0' > /sys/kernel/debug/tracing/uprobe_events
	echo 1 > /sys/kernel/debug/tracing/events/uprobes/enable
	/mnt/test

Let's split THPs before trying to replace.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Acked-by: Rik van Riel <riel@...hat.com>
Acked-by: Johannes Weiner <hannes@...xchg.org>
Cc: Oleg Nesterov <oleg@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 kernel/events/uprobes.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index d416f3baf392..1e65c79e52a6 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -300,8 +300,8 @@ int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,
 
 retry:
 	/* Read the page with vaddr into memory */
-	ret = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &old_page,
-			&vma, NULL);
+	ret = get_user_pages_remote(NULL, mm, vaddr, 1,
+			FOLL_FORCE | FOLL_SPLIT, &old_page, &vma, NULL);
 	if (ret <= 0)
 		return ret;
 
-- 
2.11.0