• Linus Torvalds's avatar
    Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk · ab486bc9
    Linus Torvalds authored
    Pull printk updates from Petr Mladek:
    
     - Add a console_msg_format command line option:
    
         The value "default" keeps the old "[time stamp] text\n" format. The
         value "syslog" allows to see the syslog-like "<log
         level>[timestamp] text" format.
    
         This feature was requested by people doing regression tests, for
         example, 0day robot. They want to have both filtered and full logs
         at hands.
    
     - Reduce the risk of softlockup:
    
         Pass the console owner in a busy loop.
    
         This is a new approach to the old problem. It was first proposed by
         Steven Rostedt on Kernel Summit 2017. It marks a context in which
         the console_lock owner calls console drivers and could not sleep.
         On the other side, printk() callers could detect this state and use
         a busy wait instead of a simple console_trylock(). Finally, the
         console_lock owner checks if there is a busy waiter at the end of
         the special context and eventually passes the console_lock to the
         waiter.
    
         The hand-off works surprisingly well and helps in many situations.
         Well, there is still a possibility of the softlockup, for example,
         when the flood of messages stops and the last owner still has too
         much to flush.
    
         There is increasing number of people having problems with
         printk-related softlockups. We might eventually need to get better
         solution. Anyway, this looks like a good start and promising
         direction.
    
     - Do not allow to schedule in console_unlock() called from printk():
    
         This reverts an older controversial commit. The reschedule helped
         to avoid softlockups. But it also slowed down the console output.
         This patch is obsoleted by the new console waiter logic described
         above. In fact, the reschedule made the hand-off less effective.
    
     - Deprecate "%pf" and "%pF" format specifier:
    
         It was needed on ia64, ppc64 and parisc64 to dereference function
         descriptors and show the real function address. It is done
         transparently by "%ps" and "pS" format specifier now.
    
         Sergey Senozhatsky found that all the function descriptors were in
         a special elf section and could be easily detected.
    
     - Remove printk_symbol() API:
    
         It has been obsoleted by "%pS" format specifier, and this change
         helped to remove few continuous lines and a less intuitive old API.
    
     - Remove redundant memsets:
    
         Sergey removed unnecessary memset when processing printk.devkmsg
         command line option.
    
    * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/pmladek/printk: (27 commits)
      printk: drop redundant devkmsg_log_str memsets
      printk: Never set console_may_schedule in console_trylock()
      printk: Hide console waiter logic into helpers
      printk: Add console owner and waiter logic to load balance console writes
      kallsyms: remove print_symbol() function
      checkpatch: add pF/pf deprecation warning
      symbol lookup: introduce dereference_symbol_descriptor()
      parisc64: Add .opd based function descriptor dereference
      powerpc64: Add .opd based function descriptor dereference
      ia64: Add .opd based function descriptor dereference
      sections: split dereference_function_descriptor()
      openrisc: Fix conflicting types for _exext and _stext
      lib: do not use print_symbol()
      irq debug: do not use print_symbol()
      sysfs: do not use print_symbol()
      drivers: do not use print_symbol()
      x86: do not use print_symbol()
      unicore32: do not use print_symbol()
      sh: do not use print_symbol()
      mn10300: do not use print_symbol()
      ...
    ab486bc9
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