[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes. |
Date: |
Mon, 18 Mar 2013 14:03:49 +0100 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Mar 18, 2013 at 12:18:43PM +0000, Alex Bligh wrote:
> Due to what is almost certainly a kernel bug, writes with
> O_DIRECT may continue to reference the page after the write
> has been marked as completed, particularly in the case of
> TCP retransmit. In other scenarios, this "merely" risks
> data corruption on the write, but with Xen pages from domU
> are only transiently mapped into dom0's memory, resulting
> in kernel panics when they are subsequently accessed.
>
> This brings PV devices in line with emulated devices. Removing
> O_DIRECT is safe as barrier operations are now correctly passed
> through.
>
> See:
> http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html
> for more details.
>From the mailing list discussion it appears that this patch is a
workaround - using the dom0 page cache to avoid the failed host kernel
paging request, which is caused by the true bug.
Has any progress been made at understanding the true problem?
> This patch has already been applied to the xenbits.org
> qemu-upstream repository.
>
> http://xenbits.xen.org/gitweb/?p=qemu-upstream-unstable.git;a=commit;h=f3903bbac78a81fcbce1350cdce860764a62783a
> Clearly it should go into qemu's own repository.
>
> Acked-by: Stefano Stabellini <address@hidden>
> Signed-off-by: Alex Bligh <address@hidden>
> ---
> hw/xen_disk.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/hw/xen_disk.c b/hw/xen_disk.c
> index a402ac8..14f8723 100644
> --- a/hw/xen_disk.c
> +++ b/hw/xen_disk.c
> @@ -603,7 +603,7 @@ static int blk_init(struct XenDevice *xendev)
> }
>
> /* read-only ? */
> - qflags = BDRV_O_NOCACHE | BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
> + qflags = BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO;
> if (strcmp(blkdev->mode, "w") == 0) {
> qflags |= BDRV_O_RDWR;
> } else {
> --
> 1.7.4.1
>
>
- [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Alex Bligh, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes.,
Stefan Hajnoczi <=
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Paolo Bonzini, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Alex Bligh, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Paolo Bonzini, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Alex Bligh, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Paolo Bonzini, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Alex Bligh, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Paolo Bonzini, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., Alex Bligh, 2013/03/18
- Re: [Qemu-devel] [PATCHv3] QEMU(upstream): Disable xen's use of O_DIRECT by default as it results in crashes., George Dunlap, 2013/03/18