• Linus Torvalds's avatar
    Merge tag 'trace-seq-buf-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace · 350e4f49
    Linus Torvalds authored
    Pull nmi-safe seq_buf printk update from Steven Rostedt:
     "This code is a fork from the trace-3.19 pull as it needed the
      trace_seq clean ups from that branch.
    
      This code solves the issue of performing stack dumps from NMI context.
      The issue is that printk() is not safe from NMI context as if the NMI
      were to trigger when a printk() was being performed, the NMI could
      deadlock from the printk() internal locks.  This has been seen in
      practice.
    
      With lots of review from Petr Mladek, this code went through several
      iterations, and we feel that it is now at a point of quality to be
      accepted into mainline.
    
      Here's what is contained in this patch set:
    
       - Creates a "seq_buf" generic buffer utility that allows a descriptor
         to be passed around where functions can write their own "printk()"
         formatted strings into it.  The generic version was pulled out of
         the trace_seq() code that was made specifically for tracing.
    
       - The seq_buf code was change to model the seq_file code.  I have a
         patch (not included for 3.19) that converts the seq_file.c code
         over to use seq_buf.c like the trace_seq.c code does.  This was
         done to make sure that seq_buf.c is compatible with seq_file.c.  I
         may try to get that patch in for 3.20.
    
       - The seq_buf.c file was moved to lib/ to remove it from being
         dependent on CONFIG_TRACING.
    
       - The printk() was updated to allow for a per_cpu "override" of the
         internal calls.  That is, instead of writing to the console, a call
         to printk() may do something else.  This made it easier to allow
         the NMI to change what printk() does in order to call dump_stack()
         without needing to update that code as well.
    
       - Finally, the dump_stack from all CPUs via NMI code was converted to
         use the seq_buf code.  The caller to trigger the NMI code would
         wait till all the NMIs finished, and then it would print the
         seq_buf data to the console safely from a non NMI context
    
      One added bonus is that this code also makes the NMI dump stack work
      on PREEMPT_RT kernels.  As printk() includes sleeping locks on
      PREEMPT_RT, printk() only writes to console if the console does not
      use any rt_mutex converted spin locks.  Which a lot do"
    
    * tag 'trace-seq-buf-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
      x86/nmi: Fix use of unallocated cpumask_var_t
      printk/percpu: Define printk_func when printk is not defined
      x86/nmi: Perform a safe NMI stack trace on all CPUs
      printk: Add per_cpu printk func to allow printk to be diverted
      seq_buf: Move the seq_buf code to lib/
      seq-buf: Make seq_buf_bprintf() conditional on CONFIG_BINARY_PRINTF
      tracing: Add seq_buf_get_buf() and seq_buf_commit() helper functions
      tracing: Have seq_buf use full buffer
      seq_buf: Add seq_buf_can_fit() helper function
      tracing: Add paranoid size check in trace_printk_seq()
      tracing: Use trace_seq_used() and seq_buf_used() instead of len
      tracing: Clean up tracing_fill_pipe_page()
      seq_buf: Create seq_buf_used() to find out how much was written
      tracing: Add a seq_buf_clear() helper and clear len and readpos in init
      tracing: Convert seq_buf fields to be like seq_file fields
      tracing: Convert seq_buf_path() to be like seq_path()
      tracing: Create seq_buf layer in trace_seq
    350e4f49
printk.c 76.4 KB