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    Subject[RFC PATCH] kmemleak: Scan all thread stacks
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    This patch changes the for_each_process() loop with the
    do_each_thread()/while_each_thread() pair. It also replaces the
    read_lock(&tasklist_lock) with rcu_read_lock() and task_lock(p).

    Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
    ---

    My questions:

    1. Is it correct that for_each_process() used currently by kmemleak may
    not loop through all the possible kernel thread stacks?

    2. Is it safe to use rcu_read_lock() and task_lock() when scanning the
    corresponding kernel stack (thread_info structure)? The loop doesn't
    do any modification to the task list. The reason for this is to
    allow kernel preemption when scanning the stacks.

    Alternatively, I can hook kmemleak callbacks into the
    alloc_thread_info/free_thread_info structures but many of these are
    architecture-specific.

    Thanks,

    Catalin


    mm/kmemleak.c | 17 ++++++++++-------
    1 files changed, 10 insertions(+), 7 deletions(-)

    diff --git a/mm/kmemleak.c b/mm/kmemleak.c
    index 983f3f6..a933128 100644
    --- a/mm/kmemleak.c
    +++ b/mm/kmemleak.c
    @@ -1064,7 +1064,6 @@ static void kmemleak_scan(void)
    {
    unsigned long flags;
    struct kmemleak_object *object, *tmp;
    - struct task_struct *task;
    int i;
    int new_leaks = 0;
    int gray_list_pass = 0;
    @@ -1135,12 +1134,16 @@ static void kmemleak_scan(void)
    * not enabled by default.
    */
    if (kmemleak_stack_scan) {
    - read_lock(&tasklist_lock);
    - for_each_process(task)
    - scan_block(task_stack_page(task),
    - task_stack_page(task) + THREAD_SIZE,
    - NULL, 0);
    - read_unlock(&tasklist_lock);
    + struct task_struct *p, *g;
    +
    + rcu_read_lock();
    + do_each_thread(g, p) {
    + task_lock(p);
    + scan_block(task_stack_page(p), task_stack_page(p) +
    + THREAD_SIZE, NULL, 0);
    + task_unlock(p);
    + } while_each_thread(g, p);
    + rcu_read_unlock();
    }

    /*


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