Eric Lee / smarc-ti-linux-kernel

05 Apr, 2011

1 commit

  • d430d3d7e   jump label: Introduce static_branch() interface ... Browse Code »

    Introduce:

    static __always_inline bool static_branch(struct jump_label_key *key);

    instead of the old JUMP_LABEL(key, label) macro.

    In this way, jump labels become really easy to use:

    Define:

    struct jump_label_key jump_key;

    Can be used as:

    if (static_branch(&jump_key))
    do unlikely code

    enable/disale via:

    jump_label_inc(&jump_key);
    jump_label_dec(&jump_key);

    that's it!

    For the jump labels disabled case, the static_branch() becomes an
    atomic_read(), and jump_label_inc()/dec() are simply atomic_inc(),
    atomic_dec() operations. We show testing results for this change below.

    Thanks to H. Peter Anvin for suggesting the 'static_branch()' construct.

    Since we now require a 'struct jump_label_key *key', we can store a pointer into
    the jump table addresses. In this way, we can enable/disable jump labels, in
    basically constant time. This change allows us to completely remove the previous
    hashtable scheme. Thanks to Peter Zijlstra for this re-write.

    Testing:

    I ran a series of 'tbench 20' runs 5 times (with reboots) for 3
    configurations, where tracepoints were disabled.

    jump label configured in
    avg: 815.6

    jump label *not* configured in (using atomic reads)
    avg: 800.1

    jump label *not* configured in (regular reads)
    avg: 803.4

    Signed-off-by: Peter Zijlstra
    LKML-Reference:
    Signed-off-by: Jason Baron
    Suggested-by: H. Peter Anvin
    Tested-by: David Daney
    Acked-by: Ralf Baechle
    Acked-by: David S. Miller
    Acked-by: Mathieu Desnoyers
    Signed-off-by: Steven Rostedt

    Jason Baron
     

30 Oct, 2010

1 commit

28 Oct, 2010

2 commits

  • 91bad2f8d   jump label: Fix deadlock b/w jump_label_mutex vs. text_mutex ... Browse Code »

    register_kprobe() downs the 'text_mutex' and then calls
    jump_label_text_reserved(), which downs the 'jump_label_mutex'.
    However, the jump label code takes those mutexes in the reverse
    order.

    Fix by requiring the caller of jump_label_text_reserved() to do
    the jump label locking via the newly added: jump_label_lock(),
    jump_label_unlock(). Currently, kprobes is the only user
    of jump_label_text_reserved().

    Reported-by: Ingo Molnar
    Acked-by: Masami Hiramatsu
    Signed-off-by: Jason Baron
    LKML-Reference:
    Signed-off-by: Steven Rostedt

    Jason Baron
     
  • b842f8faf   jump label: Fix module __init section race ... Browse Code »

    Jump label uses is_module_text_address() to ensure that the module
    __init sections are valid before updating them. However, between the
    check for a valid module __init section and the subsequent jump
    label update, the module's __init section could be freed out from under
    us.

    We fix this potential race by adding a notifier callback to the
    MODULE_STATE_LIVE state. This notifier is called *after* the __init
    section has been run but before it is going to be freed. In the
    callback, the jump label code zeros the key value for any __init jump
    code within the module, and we add a check for a non-zero key value when
    we update jump labels. In this way we require no additional data
    structures.

    Thanks to Mathieu Desnoyers for pointing out this race condition.

    Reported-by: Mathieu Desnoyers
    Cc: Masami Hiramatsu
    Signed-off-by: Jason Baron
    LKML-Reference:

    [ Renamed remove_module_init() to remove_jump_label_module_init()
    as suggested by Masami Hiramatsu. ]

    Signed-off-by: Steven Rostedt

    Jason Baron
     

23 Sep, 2010

2 commits

  • 4c3ef6d79   jump label: Add jump_label_text_reserved() to reserve jump points ... Browse Code »

    Add a jump_label_text_reserved(void *start, void *end), so that other
    pieces of code that want to modify kernel text, can first verify that
    jump label has not reserved the instruction.

    Acked-by: Masami Hiramatsu
    Signed-off-by: Jason Baron
    LKML-Reference:
    Signed-off-by: Steven Rostedt

    Jason Baron
     
  • bf5438fca   jump label: Base patch for jump label ... Browse Code »

    base patch to implement 'jump labeling'. Based on a new 'asm goto' inline
    assembly gcc mechanism, we can now branch to labels from an 'asm goto'
    statment. This allows us to create a 'no-op' fastpath, which can subsequently
    be patched with a jump to the slowpath code. This is useful for code which
    might be rarely used, but which we'd like to be able to call, if needed.
    Tracepoints are the current usecase that these are being implemented for.

    Acked-by: David S. Miller
    Signed-off-by: Jason Baron
    LKML-Reference:

    [ cleaned up some formating ]

    Signed-off-by: Steven Rostedt

    Jason Baron