Re: [Qemu-devel] [PATCH] ide: Set BSY bit during FLUSH

["Andreas Färber" <afaerber@suse.de>]

Am 28.05.2013 10:27, schrieb Kevin Wolf:
> Am 28.05.2013 um 10:18 hat Andreas Färber geschrieben:
>> The implementation of the ATA FLUSH command invokes a flush at the block
>> layer, which may on raw files on POSIX entail a synchronous fdatasync().
>> This may in some cases take so long that the SLES 11 SP1 guest driver
>> reports I/O errors and filesystems get corrupted or remounted read-only.
>>
>> Avoid this by setting BUSY_STAT, so that the guest is made aware we are
>> in the middle of an operation and no ATA commands are attempted to be
>> processed concurrently.
>>
>> Addresses BNC#637297.
>>
>> Suggested-by: Gonglei (Arei) <arei.gonglei@huawei.com>
>> Signed-off-by: Andreas Färber <afaerber@suse.de>
>> ---
>>  hw/ide/core.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/hw/ide/core.c b/hw/ide/core.c
>> index c7a8041..bf1ff18 100644
>> --- a/hw/ide/core.c
>> +++ b/hw/ide/core.c
>> @@ -795,6 +795,8 @@ static void ide_flush_cb(void *opaque, int ret)
>>  {
>>      IDEState *s = opaque;
>>  
>> +    s->status &= ~BUSY_STAT;
>> +
> 
> This part is unnecessary, the status is already reset.

Only in the ret >= 0 case though AFAICS?

>>      if (ret < 0) {
>>          /* XXX: What sector number to set here? */
>>          if (ide_handle_rw_error(s, -ret, BM_STATUS_RETRY_FLUSH)) {
>> @@ -814,6 +816,7 @@ void ide_flush_cache(IDEState *s)
>>          return;
>>      }
>>  
>> +    s->status |= BUSY_STAT;
>>      bdrv_acct_start(s->bs, &s->acct, 0, BDRV_ACCT_FLUSH);
>>      bdrv_aio_flush(s->bs, ide_flush_cb, s);
>>  }
> 
> This should fix the bug, however in an one-off way. I was planning to
> fix it by setting BSY for all commands and having an explicit command
> completion everywhere. This part is a mess currently in IDE.

That's a valid idea, but I had backporting to 0.15 in mind. ;)
And doh, I forgot qemu-stable.

> The other part why I haven't sent a fix yet is that I don't have a test
> case for it.

Temporarily add a sleep(31) in qemu_fdatasync()?

I was lazy in testing with -snapshot to not corrupt my disk image, which
would not trigger the same issue since qcow2-backed AFAIU.

> I guess I need to extend blkdebug first before this can be
> reliably tested by qtest.

It can't, since it's not a pure device emulation issue but depends on
the relative timing of filesystem operations and subsequent commands.

Andreas

-- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg