1. 23 Jul, 2013 2 commits
    • Peter Hurley's avatar
      tty: Make ldisc input flow control concurrency-friendly · 24a89d1c
      Peter Hurley authored
      Although line discipline receiving is single-producer/single-consumer,
      using tty->receive_room to manage flow control creates unnecessary
      critical regions requiring additional lock use.
      
      Instead, introduce the optional .receive_buf2() ldisc method which
      returns the # of bytes actually received. Serialization is guaranteed
      by the caller.
      
      In turn, the line discipline should schedule the buffer work item
      whenever space becomes available; ie., when there is room to receive
      data and receive_room() previously returned 0 (the buffer work
      item stops processing if receive_buf2() returns 0). Note the
      'no room' state need not be atomic despite concurrent use by two
      threads because only the buffer work thread can set the state and
      only the read() thread can clear the state.
      
      Add n_tty_receive_buf2() as the receive_buf2() method for N_TTY.
      Provide a public helper function, tty_ldisc_receive_buf(), to use
      when directly accessing the receive_buf() methods.
      
      Line disciplines not using input flow control can continue to set
      tty->receive_room to a fixed value and only provide the receive_buf()
      method.
      Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      24a89d1c
    • Peter Hurley's avatar
      tty: Replace ldisc locking with ldisc_sem · 36697529
      Peter Hurley authored
      Line discipline locking was performed with a combination of
      a mutex, a status bit, a count, and a waitqueue -- basically,
      a rw semaphore.
      
      Replace the existing combination with an ld_semaphore.
      
      Fixes:
       1) the 'reference acquire after ldisc locked' bug
       2) the over-complicated halt mechanism
       3) lock order wrt. tty_lock()
       4) dropping locks while changing ldisc
       5) previously unidentified deadlock while locking ldisc from
          both linked ttys concurrently
       6) previously unidentified recursive deadlocks
      
      Adds much-needed lockdep diagnostics.
      Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      36697529
  2. 17 Jun, 2013 1 commit
    • Peter Hurley's avatar
      n_tty: Encapsulate minimum_to_wake within N_TTY · f6c8dbe6
      Peter Hurley authored
      minimum_to_wake is unique to N_TTY processing, and belongs in
      per-ldisc data.
      
      Add the ldisc method, ldisc_ops::fasync(), to notify line disciplines
      when signal-driven I/O is enabled or disabled. When enabled for N_TTY
      (by fcntl(F_SETFL, O_ASYNC)), blocking reader/polls will be woken
      for any readable input. When disabled, blocking reader/polls are not
      woken until the read buffer is full.
      
      Canonical mode (L_ICANON(tty), n_tty_data::icanon) is not affected by
      the minimum_to_wake setting.
      Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      f6c8dbe6
  3. 20 May, 2013 1 commit
    • Peter Hurley's avatar
      tty: Add timed, writer-prioritized rw semaphore · 4898e640
      Peter Hurley authored
      The semantics of a rw semaphore are almost ideally suited
      for tty line discipline lifetime management;  multiple active
      threads obtain "references" (read locks) while performing i/o
      to prevent the loss or change of the current line discipline
      (write lock).
      
      Unfortunately, the existing rw_semaphore is ill-suited in other
      ways;
      1) TIOCSETD ioctl (change line discipline) expects to return an
         error if the line discipline cannot be exclusively locked within
         5 secs. Lock wait timeouts are not supported by rwsem.
      2) A tty hangup is expected to halt and scrap pending i/o, so
         exclusive locking must be prioritized.
         Writer priority is not supported by rwsem.
      
      Add ld_semaphore which implements these requirements in a
      semantically similar way to rw_semaphore.
      
      Writer priority is handled by separate wait lists for readers and
      writers. Pending write waits are priortized before existing read
      waits and prevent further read locks.
      
      Wait timeouts are trivially added, but obviously change the lock
      semantics as lock attempts can fail (but only due to timeout).
      
      This implementation incorporates the write-lock stealing work of
      Michel Lespinasse <walken@google.com>.
      
      Cc: Michel Lespinasse <walken@google.com>
      Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      4898e640
  4. 18 Mar, 2013 1 commit
  5. 13 Feb, 2013 1 commit
    • George Spelvin's avatar
      pps: Move timestamp read into PPS code proper · 593fb1ae
      George Spelvin authored
      The PPS (Pulse-Per-Second) line discipline has developed a number of
      unhealthy attachments to core tty data and functions, ultimately leading
      to its breakage.
      
      The previous patches fixed the crashing.  This one reduces coupling further
      by eliminating the timestamp parameter from the dcd_change ldisc method.
      This reduces header file linkage and makes the extension more generic,
      and the timestamp read is delayed only slightly, from just before the
      ldisc->ops->dcd_change method call to just after.
      
      Fix attendant build breakage in
          drivers/tty/n_tty.c
          drivers/tty/tty_buffer.c
          drivers/staging/speakup/selection.c
          drivers/staging/dgrp/dgrp_*.c
      
      Cc: William Hubbs <w.d.hubbs@gmail.com>
      Cc: Chris Brannon <chris@the-brannons.com>
      Cc: Kirk Reiser <kirk@braille.uwo.ca>
      Cc: Samuel Thibault <samuel.thibault@ens-lyon.org>
      Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
      Signed-off-by: default avatarGeorge Spelvin <linux@horizon.com>
      Acked-by: default avatarRodolfo Giometti <giometti@enneenne.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      593fb1ae
  6. 10 May, 2012 1 commit
  7. 03 Jun, 2011 1 commit
    • Linus Torvalds's avatar
      Revert "tty: make receive_buf() return the amout of bytes received" · 55db4c64
      Linus Torvalds authored
      This reverts commit b1c43f82.
      
      It was broken in so many ways, and results in random odd pty issues.
      
      It re-introduced the buggy schedule_work() in flush_to_ldisc() that can
      cause endless work-loops (see commit a5660b41: "tty: fix endless
      work loop when the buffer fills up").
      
      It also used an "unsigned int" return value fo the ->receive_buf()
      function, but then made multiple functions return a negative error code,
      and didn't actually check for the error in the caller.
      
      And it didn't actually work at all.  BenH bisected down odd tty behavior
      to it:
        "It looks like the patch is causing some major malfunctions of the X
         server for me, possibly related to PTYs.  For example, cat'ing a
         large file in a gnome terminal hangs the kernel for -minutes- in a
         loop of what looks like flush_to_ldisc/workqueue code, (some ftrace
         data in the quoted bits further down).
      
         ...
      
         Some more data: It -looks- like what happens is that the
         flush_to_ldisc work queue entry constantly re-queues itself (because
         the PTY is full ?) and the workqueue thread will basically loop
         forver calling it without ever scheduling, thus starving the consumer
         process that could have emptied the PTY."
      
      which is pretty much exactly the problem we fixed in a5660b41.
      
      Milton Miller pointed out the 'unsigned int' issue.
      Reported-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
      Reported-by: default avatarMilton Miller <miltonm@bga.com>
      Cc: Stefan Bigler <stefan.bigler@keymile.com>
      Cc: Toby Gray <toby.gray@realvnc.com>
      Cc: Felipe Balbi <balbi@ti.com>
      Cc: Greg Kroah-Hartman <gregkh@suse.de>
      Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      55db4c64
  8. 22 Apr, 2011 1 commit
  9. 13 Jan, 2011 2 commits
  10. 12 Mar, 2010 1 commit
  11. 04 Aug, 2009 1 commit
  12. 20 Jul, 2008 1 commit
    • Alan Cox's avatar
      tty: Ldisc revamp · a352def2
      Alan Cox authored
      Move the line disciplines towards a conventional ->ops arrangement.  For
      the moment the actual 'tty_ldisc' struct in the tty is kept as part of
      the tty struct but this can then be changed if it turns out that when it
      all settles down we want to refcount ldiscs separately to the tty.
      
      Pull the ldisc code out of /proc and put it with our ldisc code.
      Signed-off-by: default avatarAlan Cox <alan@redhat.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a352def2
  13. 11 May, 2007 1 commit
  14. 08 Dec, 2006 1 commit
    • Alan Cox's avatar
      [PATCH] tty: switch to ktermios and new framework · edc6afc5
      Alan Cox authored
      This is the core of the switch to the new framework.  I've split it from the
      driver patches which are mostly search/replace and would encourage people to
      give this one a good hard stare.
      
      The references to BOTHER and ISHIFT are the termios values that must be
      defined by a platform once it wants to turn on "new style" ioctl support.  The
      code patches here ensure that providing
      
      1. The termios overlays the ktermios in memory
      2. The only new kernel only fields are c_ispeed/c_ospeed (or none)
      
      the existing behaviour is retained.  This is true for the patches at this
      point in time.
      
      Future patches will define BOTHER, ISHIFT and enable newer termios structures
      for each architecture, and once they are all done some of the ifdefs also
      vanish.
      
      [akpm@osdl.org: warning fix]
      [akpm@osdl.org: IRDA fix]
      Signed-off-by: default avatarAlan Cox <alan@redhat.com>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      edc6afc5
  15. 10 Jan, 2006 1 commit
    • Alan Cox's avatar
      [PATCH] TTY layer buffering revamp · 33f0f88f
      Alan Cox authored
      The API and code have been through various bits of initial review by
      serial driver people but they definitely need to live somewhere for a
      while so the unconverted drivers can get knocked into shape, existing
      drivers that have been updated can be better tuned and bugs whacked out.
      
      This replaces the tty flip buffers with kmalloc objects in rings. In the
      normal situation for an IRQ driven serial port at typical speeds the
      behaviour is pretty much the same, two buffers end up allocated and the
      kernel cycles between them as before.
      
      When there are delays or at high speed we now behave far better as the
      buffer pool can grow a bit rather than lose characters. This also means
      that we can operate at higher speeds reliably.
      
      For drivers that receive characters in blocks (DMA based, USB and
      especially virtualisation) the layer allows a lot of driver specific
      code that works around the tty layer with private secondary queues to be
      removed. The IBM folks need this sort of layer, the smart serial port
      people do, the virtualisers do (because a virtualised tty typically
      operates at infinite speed rather than emulating 9600 baud).
      
      Finally many drivers had invalid and unsafe attempts to avoid buffer
      overflows by directly invoking tty methods extracted out of the innards
      of work queue structs. These are no longer needed and all go away. That
      fixes various random hangs with serial ports on overflow.
      
      The other change in here is to optimise the receive_room path that is
      used by some callers. It turns out that only one ldisc uses receive room
      except asa constant and it updates it far far less than the value is
      read. We thus make it a variable not a function call.
      
      I expect the code to contain bugs due to the size alone but I'll be
      watching and squashing them and feeding out new patches as it goes.
      
      Because the buffers now dynamically expand you should only run out of
      buffering when the kernel runs out of memory for real.  That means a lot of
      the horrible hacks high performance drivers used to do just aren't needed any
      more.
      
      Description:
      
      tty_insert_flip_char is an old API and continues to work as before, as does
      tty_flip_buffer_push() [this is why many drivers dont need modification].  It
      does now also return the number of chars inserted
      
      There are also
      
      tty_buffer_request_room(tty, len)
      
      which asks for a buffer block of the length requested and returns the space
      found.  This improves efficiency with hardware that knows how much to
      transfer.
      
      and tty_insert_flip_string_flags(tty, str, flags, len)
      
      to insert a string of characters and flags
      
      For a smart interface the usual code is
      
          len = tty_request_buffer_room(tty, amount_hardware_says);
          tty_insert_flip_string(tty, buffer_from_card, len);
      
      More description!
      
      At the moment tty buffers are attached directly to the tty.  This is causing a
      lot of the problems related to tty layer locking, also problems at high speed
      and also with bursty data (such as occurs in virtualised environments)
      
      I'm working on ripping out the flip buffers and replacing them with a pool of
      dynamically allocated buffers.  This allows both for old style "byte I/O"
      devices and also helps virtualisation and smart devices where large blocks of
      data suddenely materialise and need storing.
      
      So far so good.  Lots of drivers reference tty->flip.*.  Several of them also
      call directly and unsafely into function pointers it provides.  This will all
      break.  Most drivers can use tty_insert_flip_char which can be kept as an API
      but others need more.
      
      At the moment I've added the following interfaces, if people think more will
      be needed now is a good time to say
      
       int tty_buffer_request_room(tty, size)
      
      Try and ensure at least size bytes are available, returns actual room (may be
      zero).  At the moment it just uses the flipbuf space but that will change.
      Repeated calls without characters being added are not cumulative.  (ie if you
      call it with 1, 1, 1, and then 4 you'll have four characters of space.  The
      other functions will also try and grow buffers in future but this will be a
      more efficient way when you know block sizes.
      
       int tty_insert_flip_char(tty, ch, flag)
      
      As before insert a character if there is room.  Now returns 1 for success, 0
      for failure.
      
       int tty_insert_flip_string(tty, str, len)
      
      Insert a block of non error characters.  Returns the number inserted.
      
       int tty_prepare_flip_string(tty, strptr, len)
      
      Adjust the buffer to allow len characters to be added.  Returns a buffer
      pointer in strptr and the length available.  This allows for hardware that
      needs to use functions like insl or mencpy_fromio.
      Signed-off-by: default avatarAlan Cox <alan@redhat.com>
      Cc: Paul Fulghum <paulkf@microgate.com>
      Signed-off-by: default avatarHirokazu Takata <takata@linux-m32r.org>
      Signed-off-by: default avatarSerge Hallyn <serue@us.ibm.com>
      Signed-off-by: default avatarJeff Dike <jdike@addtoit.com>
      Signed-off-by: default avatarJohn Hawkes <hawkes@sgi.com>
      Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
      Signed-off-by: default avatarAdrian Bunk <bunk@stusta.de>
      Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
      33f0f88f
  16. 16 Apr, 2005 1 commit
    • Linus Torvalds's avatar
      Linux-2.6.12-rc2 · 1da177e4
      Linus Torvalds authored
      Initial git repository build. I'm not bothering with the full history,
      even though we have it. We can create a separate "historical" git
      archive of that later if we want to, and in the meantime it's about
      3.2GB when imported into git - space that would just make the early
      git days unnecessarily complicated, when we don't have a lot of good
      infrastructure for it.
      
      Let it rip!
      1da177e4