From 7137c6bd455234bcb7560fd829e6ee49cae5fed6 Mon Sep 17 00:00:00 2001
From: Jan Kara <jack@suse.cz>
Date: Fri, 25 Feb 2011 14:44:27 -0800
Subject: [PATCH] aio: fix race between io_destroy() and io_submit()

A race can occur when io_submit() races with io_destroy():

 CPU1						CPU2
io_submit()
  do_io_submit()
    ...
    ctx = lookup_ioctx(ctx_id);
						io_destroy()
    Now do_io_submit() holds the last reference to ctx.
    ...
    queue new AIO
    put_ioctx(ctx) - frees ctx with active AIOs

We solve this issue by checking whether ctx is being destroyed in AIO
submission path after adding new AIO to ctx.  Then we are guaranteed that
either io_destroy() waits for new AIO or we see that ctx is being
destroyed and bail out.

Cc: Nick Piggin <npiggin@kernel.dk>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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