1. 23 Aug, 2014 1 commit
    • Steven Rostedt (Red Hat)'s avatar
      ftrace: Fix function_profiler and function tracer together · 5f151b24
      Steven Rostedt (Red Hat) authored
      The latest rewrite of ftrace removed the separate ftrace_ops of
      the function tracer and the function graph tracer and had them
      share the same ftrace_ops. This simplified the accounting by removing
      the multiple layers of functions called, where the global_ops func
      would call a special list that would iterate over the other ops that
      were registered within it (like function and function graph), which
      itself was registered to the ftrace ops list of all functions
      currently active. If that sounds confusing, the code that implemented
      it was also confusing and its removal is a good thing.
      The problem with this change was that it assumed that the function
      and function graph tracer can never be used at the same time.
      This is mostly true, but there is an exception. That is when the
      function profiler uses the function graph tracer to profile.
      The function profiler can be activated the same time as the function
      tracer, and this breaks the assumption and the result is that ftrace
      will crash (it detects the error and shuts itself down, it does not
      cause a kernel oops).
      To solve this issue, a previous change allowed the hash tables
      for the functions traced by a ftrace_ops to be a pointer and let
      multiple ftrace_ops share the same hash. This allows the function
      and function_graph tracer to have separate ftrace_ops, but still
      share the hash, which is what is done.
      Now the function and function graph tracers have separate ftrace_ops
      again, and the function tracer can be run while the function_profile
      is active.
      Cc: stable@vger.kernel.org # 3.16 (apply after 3.17-rc4 is out)
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
  2. 22 Aug, 2014 3 commits
    • Steven Rostedt (Red Hat)'s avatar
      ftrace: Fix up trampoline accounting with looping on hash ops · bce0b6c5
      Steven Rostedt (Red Hat) authored
      Now that a ftrace_hash can be shared by multiple ftrace_ops, they can dec
      the rec->flags by more than once (one per those that share the ftrace_hash).
      This means that the tramp_hash may not have a hash item when it was added.
      For example, if two ftrace_ops share a hash for a ftrace record, and the
      first ops has a trampoline, when it adds itself it will set the rec->flags
      TRAMP flag and increments its nr_trampolines counter. When the second ops
      is added, it must clear that tramp flag but also decrement the other ops
      that shares its hash. As the update to the function callbacks has not yet
      been performed, the other ops will not have the tramp hash set yet and it
      can not be used to know to decrement its nr_trampolines.
      Luckily, the tramp_hash does not need to be used. As the ftrace_mutex is
      held, a ops with a trampoline to a record during an update of another ops
      that shares the record will have its func_hash pointing to it. Since a
      trampoline can only be set for a record if only one ops is attached to it,
      we can just check if the record has a trampoline (the FTRACE_FL_TRAMP flag
      is set) and then find the ops that has this record in its hashes.
      Also added some output to help debug when things go wrong.
      Cc: stable@vger.kernel.org # 3.16+ (apply after 3.17-rc4 is out)
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    • Steven Rostedt (Red Hat)'s avatar
      ftrace: Update all ftrace_ops for a ftrace_hash_ops update · 84261912
      Steven Rostedt (Red Hat) authored
      When updating what an ftrace_ops traces, if it is registered (that is,
      actively tracing), and that ftrace_ops uses the shared global_ops
      local_hash, then we need to update all tracers that are active and
      also share the global_ops' ftrace_hash_ops.
      Cc: stable@vger.kernel.org # 3.16 (apply after 3.17-rc4 is out)
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
    • Steven Rostedt (Red Hat)'s avatar
      ftrace: Allow ftrace_ops to use the hashes from other ops · 33b7f99c
      Steven Rostedt (Red Hat) authored
      Currently the top level debug file system function tracer shares its
      ftrace_ops with the function graph tracer. This was thought to be fine
      because the tracers are not used together, as one can only enable
      function or function_graph tracer in the current_tracer file.
      But that assumption proved to be incorrect. The function profiler
      can use the function graph tracer when function tracing is enabled.
      Since all function graph users uses the function tracing ftrace_ops
      this causes a conflict and when a user enables both function profiling
      as well as the function tracer it will crash ftrace and disable it.
      The quick solution so far is to move them as separate ftrace_ops like
      it was earlier. The problem though is to synchronize the functions that
      are traced because both function and function_graph tracer are limited
      by the selections made in the set_ftrace_filter and set_ftrace_notrace
      To handle this, a new structure is made called ftrace_ops_hash. This
      structure will now hold the filter_hash and notrace_hash, and the
      ftrace_ops will point to this structure. That will allow two ftrace_ops
      to share the same hashes.
      Since most ftrace_ops do not share the hashes, and to keep allocation
      simple, the ftrace_ops structure will include both a pointer to the
      ftrace_ops_hash called func_hash, as well as the structure itself,
      called local_hash. When the ops are registered, the func_hash pointer
      will be initialized to point to the local_hash within the ftrace_ops
      structure. Some of the ftrace internal ftrace_ops will be initialized
      statically. This will allow for the function and function_graph tracer
      to have separate ops but still share the same hash tables that determine
      what functions they trace.
      Cc: stable@vger.kernel.org # 3.16 (apply after 3.17-rc4 is out)
      Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
  3. 16 Aug, 2014 36 commits