Re: [Qemu-devel] IDE disk FLUSH take more than 30 secs, the SUSE guest reports "lost interrupt and the file system becomes read-only"

[Andreas Färber]

Am 21.05.2013 09:12, schrieb Gonglei (Arei):
> Through analysis, I found that because the system call the fdatasync command 
> in the Qemu over 30s, 
> after the Guest's kernel thread detects the io transferation is timeout, went 
> to check IDE disk state. 
> But the IDE disk status is 0x50, rather than the BSY status, and then 
> departed error process...
> 
> the path of kernel's action is :
> scsi_softirq_done
>  scsi_eh_scmd_add
>    scsi_error_handler
>      shost->transportt->eh_strategy_handler 
>               ata_scsi_error 
>                       ap->ops->lost_interrupt
>                               ata_sff_lost_interrupt
> Finally, the file system becomes read-only.
> 
> Why not set the IDE disk for the BSY status When 0xe7 command is executed in 
> the Qemu?

Have you actually tried that out with a patch such as the following?

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;
+
     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);
 }

No clue if this is spec-compliant. ;)

Note however that qemu_fdatasync() is done in the flush callback of
block/raw-posix.c, so IIUC everything calling bdrv_aio_flush() or
bdrv_flush_all() may potentially run into issues beyond just ATA:

hw/block/virtio-blk.c
hw/block/xen_disk.c
hw/ide/core.c
hw/scsi/scsi-disk.c

cpus.c:do_vm_stop()
hw/xen/xen_platform.c:platform_fixed_ioport_writew()

qemu_fdatasync() further occurs in:

hw/block/dataplane/virtio-blk.c:process_request()
hw/9pfs/virtio-9p-*.c

Quite possibly not all of them are problematic, but flush times >30 sec
are very likely not well tested by developers...

Regards,
Andreas

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