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    Subject[Patch 1/2] Improvements and minor fixes to HW Breakpoint interface
    This patch brings a couple of changes to the HW Breakpoint infrastructure:

    - Set/clear TIF_DEBUG task flag in <un>register_user_hw_breakpoint()
    instead of being done by users of this interface (such as ptrace).

    - Modify return code of hw_breakpoint_handler() to NOTIFY_STOP if
    triggered due to lazy debug register switching.

    Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
    ---
    arch/x86/kernel/hw_breakpoint.c | 4 +++-
    arch/x86/kernel/ptrace.c | 4 +---
    kernel/hw_breakpoint.c | 16 +++++++++++++---
    3 files changed, 17 insertions(+), 7 deletions(-)

    Index: linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
    ===================================================================
    --- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/hw_breakpoint.c
    +++ linux-2.6-tip.hbkpt/arch/x86/kernel/hw_breakpoint.c
    @@ -346,8 +346,10 @@ int __kprobes hw_breakpoint_handler(stru
    * or due to the delay between updates of hbp_kernel_pos
    * and this_hbp_kernel.
    */
    - if (!bp)
    + if (!bp) {
    + rc = NOTIFY_STOP;
    continue;
    + }

    (bp->triggered)(bp, args->regs);
    /*
    Index: linux-2.6-tip.hbkpt/arch/x86/kernel/ptrace.c
    ===================================================================
    --- linux-2.6-tip.hbkpt.orig/arch/x86/kernel/ptrace.c
    +++ linux-2.6-tip.hbkpt/arch/x86/kernel/ptrace.c
    @@ -530,9 +530,7 @@ restore:
    bp->info.len = len;
    bp->info.type = type;
    rc = register_user_hw_breakpoint(tsk, bp);
    - if (!rc)
    - set_tsk_thread_flag(tsk, TIF_DEBUG);
    - else
    + if (rc)
    kfree(bp);
    }
    } else
    Index: linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
    ===================================================================
    --- linux-2.6-tip.hbkpt.orig/kernel/hw_breakpoint.c
    +++ linux-2.6-tip.hbkpt/kernel/hw_breakpoint.c
    @@ -233,6 +233,8 @@ int register_user_hw_breakpoint(struct t
    break;
    }
    }
    + if (!rc)
    + set_tsk_thread_flag(tsk, TIF_DEBUG);

    spin_unlock_bh(&hw_breakpoint_lock);
    return rc;
    @@ -272,15 +274,23 @@ void unregister_user_hw_breakpoint(struc
    struct hw_breakpoint *bp)
    {
    struct thread_struct *thread = &(tsk->thread);
    - int i;
    + int i, pos = -1, clear_tsk_debug_counter = 0;

    spin_lock_bh(&hw_breakpoint_lock);
    for (i = 0; i < hbp_kernel_pos; i++) {
    + if (thread->hbp[i])
    + clear_tsk_debug_counter++;
    if (bp == thread->hbp[i]) {
    - __unregister_user_hw_breakpoint(i, tsk);
    - break;
    + clear_tsk_debug_counter--;
    + pos = i;
    }
    }
    + if (pos >= 0)
    + __unregister_user_hw_breakpoint(pos, tsk);
    +
    + if (!clear_tsk_debug_counter)
    + clear_tsk_thread_flag(tsk, TIF_DEBUG);
    +
    spin_unlock_bh(&hw_breakpoint_lock);
    }
    EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint);


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