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Re: [Qemu-block] [PATCH v4] linux-aio: properly bubble up errors from in
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-block] [PATCH v4] linux-aio: properly bubble up errors from initialization |
Date: |
Wed, 27 Jun 2018 13:06:51 +0100 |
User-agent: |
Mutt/1.10.0 (2018-05-17) |
On Fri, Jun 22, 2018 at 12:37:00PM -0700, Nishanth Aravamudan wrote:
> laio_init() can fail for a couple of reasons, which will lead to a NULL
> pointer dereference in laio_attach_aio_context().
>
> To solve this, add a aio_setup_linux_aio() function which is called
> early in raw_open_common. If this fails, propagate the error up. The
> signature of aio_get_linux_aio() was not modified, because it seems
> preferable to return the actual errno from the possible failing
> initialization calls.
>
> Additionally, when the AioContext changes, we need to associate a
> LinuxAioState with the new AioContext. Use the bdrv_attach_aio_context
> callback and call the new aio_setup_linux_aio(), which will allocate a
> new AioContext if needed, and return errors on failures. If it fails for
> any reason, fallback to threaded AIO with an error message, as the
> device is already in-use by the guest.
>
> Add an assert that aio_get_linux_aio() cannot return NULL.
>
> Signed-off-by: Nishanth Aravamudan <address@hidden>
>
> ---
>
> Test case 1:
> Set /proc/sys/fs/max-aio-nr to 0. Start a guest with an aio=native
> disk.
>
> Result: laio_init() returns NULL due to not being able to allocate
> any AIO contexts. This NULL is assigned to ctx->linux_aio and
> dereferenced in aio_get_linux_aio.
>
> Test case 2:
> Set /proc/sys/fs/max-aio-nr to 128. Start a guest with an aio=native
> disk and one in-use I/O thread.
>
> Result: laio_init() returns NULL due to not being able to allocate
> additional AIO contexts for the I/O thread. This NULL is assigned to
> ctx->linux_aio and dereferenced in aio_get_linux_aio.
>
> Changes from v3 -> v4 (thanks to Fam Zheng and Kevin Wolf for review):
>
> Squash patch 2/2 into 1/2.
> Differentiate the possible reasons for laio_init() failing and use an
> Error ** to propagate the errno to the caller.
>
> Changes from v2 -> v3 (thanks to Eric Blake and Kevin Wolf for review):
>
> Use a boolean false rather than 0 in assignment to use_linux_aio.
> Drop ending '.' from error_report() calls.
> Fix typo in commit message (propogates -> propagates).
> Move aio_setup_linux_aio call to raw_open_common.
>
> Changes from v1 -> v2 (thanks to Kevin Wolf for review):
>
> Rather than affect virtio-scsi/blk at all, make all the changes internal
> to file-posix.c. Thanks to Kevin Wolf for the suggested change.
>
> block/file-posix.c | 33 ++++++++++++++++++++++++++++-----
> block/linux-aio.c | 12 +++++++++---
> include/block/aio.h | 3 +++
> include/block/raw-aio.h | 2 +-
> stubs/linux-aio.c | 2 +-
> util/async.c | 14 +++++++++++---
> 6 files changed, 53 insertions(+), 13 deletions(-)
Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block
Stefan
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