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    Subject[tip:perf/core] uprobes: Change read_opcode() to use FOLL_FORCE
    Commit-ID:  a3d7bb47937b3a40b9f0c75655e97b3bb6407cbe
    Gitweb: http://git.kernel.org/tip/a3d7bb47937b3a40b9f0c75655e97b3bb6407cbe
    Author: Oleg Nesterov <oleg@redhat.com>
    AuthorDate: Tue, 29 May 2012 21:27:59 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Wed, 6 Jun 2012 17:14:49 +0200

    uprobes: Change read_opcode() to use FOLL_FORCE

    set_orig_insn()->read_opcode() should not fail if the probed
    task did mprotect() after uprobe_register(), change it to use
    FOLL_FORCE. Without FOLL_WRITE this doesn't have any "side"
    effect but allows to read the !VM_READ memory.

    There is another reason for this change, we are going to use
    is_swbp_at_addr() from handle_swbp() which can race with another
    thread doing mprotect().

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Anton Arapov <anton@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/20120529192759.GB8057@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/events/uprobes.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    index d0f5ec0..a0dbc87 100644
    --- a/kernel/events/uprobes.c
    +++ b/kernel/events/uprobes.c
    @@ -312,7 +312,7 @@ static int read_opcode(struct mm_struct *mm, unsigned long vaddr, uprobe_opcode_
    void *vaddr_new;
    int ret;

    - ret = get_user_pages(NULL, mm, vaddr, 1, 0, 0, &page, NULL);
    + ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
    if (ret <= 0)
    return ret;


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