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    Subject[tip:perf/core] uprobes: Move BUG_ON(UPROBE_SWBP_INSN_SIZE) from write_opcode() to install_breakpoint()
    Commit-ID:  d9c4a30e82614d43b55893a73f31e7284007ce82
    Gitweb: http://git.kernel.org/tip/d9c4a30e82614d43b55893a73f31e7284007ce82
    Author: Oleg Nesterov <oleg@redhat.com>
    AuthorDate: Fri, 15 Jun 2012 17:43:50 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Sat, 16 Jun 2012 09:10:47 +0200

    uprobes: Move BUG_ON(UPROBE_SWBP_INSN_SIZE) from write_opcode() to install_breakpoint()

    write_opcode() ensures that UPROBE_SWBP_INSN doesn't cross the
    page boundary. This looks a bit confusing, the check does not
    depend on vaddr and it is enough to do it only once right after
    install_breakpoint()->arch_uprobe_analyze_insn().

    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    Cc: Anton Arapov <anton@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Link: http://lkml.kernel.org/r/20120615154350.GA9611@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/events/uprobes.c | 11 +++++------
    1 files changed, 5 insertions(+), 6 deletions(-)

    diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
    index 14c71a2..b9c61bd 100644
    --- a/kernel/events/uprobes.c
    +++ b/kernel/events/uprobes.c
    @@ -210,7 +210,6 @@ static int write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
    void *vaddr_old, *vaddr_new;
    struct vm_area_struct *vma;
    struct uprobe *uprobe;
    - unsigned long pgoff;
    int ret;
    retry:
    /* Read the page with vaddr into memory */
    @@ -251,11 +250,7 @@ retry:
    vaddr_new = kmap_atomic(new_page);

    memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
    -
    - /* poke the new insn in, ASSUMES we don't cross page boundary */
    - pgoff = (vaddr & ~PAGE_MASK);
    - BUG_ON(pgoff + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
    - memcpy(vaddr_new + pgoff, &opcode, UPROBE_SWBP_INSN_SIZE);
    + memcpy(vaddr_new + (vaddr & ~PAGE_MASK), &opcode, UPROBE_SWBP_INSN_SIZE);

    kunmap_atomic(vaddr_new);
    kunmap_atomic(vaddr_old);
    @@ -699,6 +694,10 @@ install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
    if (ret)
    return ret;

    + /* write_opcode() assumes we don't cross page boundary */
    + BUG_ON((uprobe->offset & ~PAGE_MASK) +
    + UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
    +
    uprobe->flags |= UPROBE_COPY_INSN;
    }


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