tree 125b3e69a5c5393cb0db622f7c3a7f1893f9f9ea
parent a29a37b994ca3c5a1d39fa0e8934f7e0f2cf57ef
author Markus Armbruster <armbru@redhat.com> 1441983103 +0200
committer Markus Armbruster <armbru@redhat.com> 1442579969 +0200

Fix bad error handling after memory_region_init_ram()

Symptom:

    $ qemu-system-x86_64 -m 10000000
    Unexpected error in ram_block_add() at /work/armbru/qemu/exec.c:1456:
    upstream-qemu: cannot set up guest memory 'pc.ram': Cannot allocate memory
    Aborted (core dumped)

Root cause: commit ef701d7 screwed up handling of out-of-memory
conditions.  Before the commit, we report the error and exit(1), in
one place, ram_block_add().  The commit lifts the error handling up
the call chain some, to three places.  Fine.  Except it uses
&error_abort in these places, changing the behavior from exit(1) to
abort(), and thus undoing the work of commit 3922825 "exec: Don't
abort when we can't allocate guest memory".

The three places are:

* memory_region_init_ram()

  Commit 4994653 (right after commit ef701d7) lifted the error
  handling further, through memory_region_init_ram(), multiplying the
  incorrect use of &error_abort.  Later on, imitation of existing
  (bad) code may have created more.

* memory_region_init_ram_ptr()

  The &error_abort is still there.

* memory_region_init_rom_device()

  Doesn't need fixing, because commit 33e0eb5 (soon after commit
  ef701d7) lifted the error handling further, and in the process
  changed it from &error_abort to passing it up the call chain.
  Correct, because the callers are realize() methods.

Fix the error handling after memory_region_init_ram() with a
Coccinelle semantic patch:

    @r@
    expression mr, owner, name, size, err;
    position p;
    @@
            memory_region_init_ram(mr, owner, name, size,
    (
    -                              &error_abort
    +                              &error_fatal
    |
                                   err@p
    )
                                  );
    @script:python@
        p << r.p;
    @@
    print "%s:%s:%s" % (p[0].file, p[0].line, p[0].column)

When the last argument is &error_abort, it gets replaced by
&error_fatal.  This is the fix.

If the last argument is anything else, its position is reported.  This
lets us check the fix is complete.  Four positions get reported:

* ram_backend_memory_alloc()

  Error is passed up the call chain, ultimately through
  user_creatable_complete().  As far as I can tell, it's callers all
  handle the error sanely.

* fsl_imx25_realize(), fsl_imx31_realize(), dp8393x_realize()

  DeviceClass.realize() methods, errors handled sanely further up the
  call chain.

We're good.  Test case again behaves:

    $ qemu-system-x86_64 -m 10000000
    qemu-system-x86_64: cannot set up guest memory 'pc.ram': Cannot allocate memory
    [Exit 1 ]

The next commits will repair the rest of commit ef701d7's damage.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1441983105-26376-3-git-send-email-armbru@redhat.com>
Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>