[PATCH] AIO: retry infrastructure fixes and enhancements

[PATCH] AIO: retry infrastructure fixes and enhancements

From: Daniel McNeil <daniel@osdl.org>
From: Chris Mason <mason@suse.com>

 AIO: retry infrastructure fixes and enhancements

 Reorganises, comments and fixes the AIO retry logic. Fixes
 and enhancements include:

   - Split iocb setup and execution in io_submit
        (also fixes io_submit error reporting)
   - Use aio workqueue instead of keventd for retries
   - Default high level retry methods
   - Subtle use_mm/unuse_mm fix
   - Code commenting
   - Fix aio process hang on EINVAL (Daniel McNeil)
   - Hold the context lock across unuse_mm
   - Acquire task_lock in use_mm()
   - Allow fops to override the retry method with their own
   - Elevated ref count for AIO retries (Daniel McNeil)
   - set_fs needed when calling use_mm
   - Flush workqueue on __put_ioctx (Chris Mason)
   - Fix io_cancel to work with retries (Chris Mason)
   - Read-immediate option for socket/pipe retry support

 Note on default high-level retry methods support
 ================================================

 High-level retry methods allows an AIO request to be executed as a series of
 non-blocking iterations, where each iteration retries the remaining part of
 the request from where the last iteration left off, by reissuing the
 corresponding AIO fop routine with modified arguments representing the
 remaining I/O.  The retries are "kicked" via the AIO waitqueue callback
 aio_wake_function() which replaces the default wait queue entry used for
 blocking waits.

 The high level retry infrastructure is responsible for running the
 iterations in the mm context (address space) of the caller, and ensures that
 only one retry instance is active at a given time, thus relieving the fops
 themselves from having to deal with potential races of that sort.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>