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    Subject[patch 01/11] Kprobes - use a mutex to protect the instruction pages list.
    Protect the instruction pages list by a specific insn pages mutex, called in 
    get_insn_slot() and free_insn_slot(). It makes sure that architectures that does
    not need to call arch_remove_kprobe() does not take an unneeded kprobes mutex.

    Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
    CC: hch@infradead.org
    CC: prasanna@in.ibm.com
    CC: anil.s.keshavamurthy@intel.com
    CC: davem@davemloft.net
    ---
    kernel/kprobes.c | 27 +++++++++++++++++++++------
    1 file changed, 21 insertions(+), 6 deletions(-)

    Index: linux-2.6-lttng/kernel/kprobes.c
    ===================================================================
    --- linux-2.6-lttng.orig/kernel/kprobes.c 2007-08-27 11:48:56.000000000 -0400
    +++ linux-2.6-lttng/kernel/kprobes.c 2007-08-27 11:48:58.000000000 -0400
    @@ -95,6 +95,10 @@ enum kprobe_slot_state {
    SLOT_USED = 2,
    };

    +/*
    + * Protects the kprobe_insn_pages list. Can nest into kprobe_mutex.
    + */
    +static DEFINE_MUTEX(kprobe_insn_mutex);
    static struct hlist_head kprobe_insn_pages;
    static int kprobe_garbage_slots;
    static int collect_garbage_slots(void);
    @@ -131,7 +135,9 @@ kprobe_opcode_t __kprobes *get_insn_slot
    {
    struct kprobe_insn_page *kip;
    struct hlist_node *pos;
    + kprobe_opcode_t *ret;

    + mutex_lock(&kprobe_insn_mutex);
    retry:
    hlist_for_each_entry(kip, pos, &kprobe_insn_pages, hlist) {
    if (kip->nused < INSNS_PER_PAGE) {
    @@ -140,7 +146,8 @@ kprobe_opcode_t __kprobes *get_insn_slot
    if (kip->slot_used[i] == SLOT_CLEAN) {
    kip->slot_used[i] = SLOT_USED;
    kip->nused++;
    - return kip->insns + (i * MAX_INSN_SIZE);
    + ret = kip->insns + (i * MAX_INSN_SIZE);
    + goto end;
    }
    }
    /* Surprise! No unused slots. Fix kip->nused. */
    @@ -154,8 +161,10 @@ kprobe_opcode_t __kprobes *get_insn_slot
    }
    /* All out of space. Need to allocate a new page. Use slot 0. */
    kip = kmalloc(sizeof(struct kprobe_insn_page), GFP_KERNEL);
    - if (!kip)
    - return NULL;
    + if (!kip) {
    + ret = NULL;
    + goto end;
    + }

    /*
    * Use module_alloc so this page is within +/- 2GB of where the
    @@ -165,7 +174,8 @@ kprobe_opcode_t __kprobes *get_insn_slot
    kip->insns = module_alloc(PAGE_SIZE);
    if (!kip->insns) {
    kfree(kip);
    - return NULL;
    + ret = NULL;
    + goto end;
    }
    INIT_HLIST_NODE(&kip->hlist);
    hlist_add_head(&kip->hlist, &kprobe_insn_pages);
    @@ -173,7 +183,10 @@ kprobe_opcode_t __kprobes *get_insn_slot
    kip->slot_used[0] = SLOT_USED;
    kip->nused = 1;
    kip->ngarbage = 0;
    - return kip->insns;
    + ret = kip->insns;
    +end:
    + mutex_unlock(&kprobe_insn_mutex);
    + return ret;
    }

    /* Return 1 if all garbages are collected, otherwise 0. */
    @@ -207,7 +220,7 @@ static int __kprobes collect_garbage_slo
    struct kprobe_insn_page *kip;
    struct hlist_node *pos, *next;

    - /* Ensure no-one is preepmted on the garbages */
    + /* Ensure no-one is preempted on the garbages */
    if (check_safety() != 0)
    return -EAGAIN;

    @@ -231,6 +244,7 @@ void __kprobes free_insn_slot(kprobe_opc
    struct kprobe_insn_page *kip;
    struct hlist_node *pos;

    + mutex_lock(&kprobe_insn_mutex);
    hlist_for_each_entry(kip, pos, &kprobe_insn_pages, hlist) {
    if (kip->insns <= slot &&
    slot < kip->insns + (INSNS_PER_PAGE * MAX_INSN_SIZE)) {
    @@ -247,6 +261,7 @@ void __kprobes free_insn_slot(kprobe_opc

    if (dirty && ++kprobe_garbage_slots > INSNS_PER_PAGE)
    collect_garbage_slots();
    + mutex_unlock(&kprobe_insn_mutex);
    }
    #endif

    --
    Mathieu Desnoyers
    Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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