• Linus Torvalds's avatar
    Merge tag 'notifications-pipe-prep-20191115' of... · 6a965666
    Linus Torvalds authored
    Merge tag 'notifications-pipe-prep-20191115' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs
    
    Pull pipe rework from David Howells:
     "This is my set of preparatory patches for building a general
      notification queue on top of pipes. It makes a number of significant
      changes:
    
       - It removes the nr_exclusive argument from __wake_up_sync_key() as
         this is always 1. This prepares for the next step:
    
       - Adds wake_up_interruptible_sync_poll_locked() so that poll can be
         woken up from a function that's holding the poll waitqueue
         spinlock.
    
       - Change the pipe buffer ring to be managed in terms of unbounded
         head and tail indices rather than bounded index and length. This
         means that reading the pipe only needs to modify one index, not
         two.
    
       - A selection of helper functions are provided to query the state of
         the pipe buffer, plus a couple to apply updates to the pipe
         indices.
    
       - The pipe ring is allowed to have kernel-reserved slots. This allows
         many notification messages to be spliced in by the kernel without
         allowing userspace to pin too many pages if it writes to the same
         pipe.
    
       - Advance the head and tail indices inside the pipe waitqueue lock
         and use wake_up_interruptible_sync_poll_locked() to poke poll
         without having to take the lock twice.
    
       - Rearrange pipe_write() to preallocate the buffer it is going to
         write into and then drop the spinlock. This allows kernel
         notifications to then be added the ring whilst it is filling the
         buffer it allocated. The read side is stalled because the pipe
         mutex is still held.
    
       - Don't wake up readers on a pipe if there was already data in it
         when we added more.
    
       - Don't wake up writers on a pipe if the ring wasn't full before we
         removed a buffer"
    
    * tag 'notifications-pipe-prep-20191115' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
      pipe: Remove sync on wake_ups
      pipe: Increase the writer-wakeup threshold to reduce context-switch count
      pipe: Check for ring full inside of the spinlock in pipe_write()
      pipe: Remove redundant wakeup from pipe_write()
      pipe: Rearrange sequence in pipe_write() to preallocate slot
      pipe: Conditionalise wakeup in pipe_read()
      pipe: Advance tail pointer inside of wait spinlock in pipe_read()
      pipe: Allow pipes to have kernel-reserved slots
      pipe: Use head and tail pointers for the ring, not cursor and length
      Add wake_up_interruptible_sync_poll_locked()
      Remove the nr_exclusive argument from __wake_up_sync_key()
      pipe: Reduce #inclusion of pipe_fs_i.h
    6a965666