Re: [Qemu-devel] "block: use aio_bh_schedule_oneshot" breaks ibm-vscsi

[Paolo Bonzini <pbonzini@redhat.com>]

On 27/10/2016 05:30, Alexey Kardashevskiy wrote:
> Hi,
> 
> I just discovered that fffb6e12233002c26c0ee9ff92fa87927cd779f2 broke
> ibm-vscsi, the guest booting stops (I waited for a minute) at:
> 
> [    0.809286] ibmvscsi 71000001: SRP_VERSION: 16.a
> [    0.809766] ibmvscsi 71000001: Maximum ID: 64 Maximum LUN: 32 Maximum Channel: 3
> [    0.810059] scsi host0: IBM POWER Virtual SCSI Adapter 1.5.9
> [    0.810634] ibmvscsi 71000001: partner initialization complete
> [    0.810999] ibmvscsi 71000001: host srp version: 16.a, host partition qemu (0), OS 2, max io 2097152
> [    0.811507] ibmvscsi 71000001: sent SRP login
> [    0.811705] ibmvscsi 71000001: SRP_LOGIN succeeded
> [    0.824062] scsi 0:0:0:0: Direct-Access     QEMU     QEMU HARDDISK    2.5+ PQ: 0 ANSI: 5
> [    1.018526] sd 0:0:0:0: Attached scsi generic sg0 type 0
> [    1.019352] sd 0:0:0:0: [sda] 67108864 512-byte logical blocks: (34.4 GB/32.0 GiB)
> [    1.020274] sd 0:0:0:0: [sda] Write Protect is off
> [    1.020667] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
> [    1.023390]  sda: sda1 sda2 sda3
> [    1.025819] sd 0:0:0:0: [sda] Attached SCSI disk
> 
> 
> When I switch to virtio-vscsi, I get a bit further:
> 
> Begin: Loading essential drivers ... done.
> Begin: Running /scripts/init-premount ... done.
> Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done.
> Begin: Running /scripts/local-premount ... done.
> Begin: Will now check root file system ... fsck from util-linux 2.27.1
> [/sbin/fsck.ext4 (1) -- /dev/sda2] fsck.ext4 -a -C0 /dev/sda2
> fsck.ext4: Read-only file system while trying to open /dev/sda2
> Disk write-protected; use the -n option to do a read-only
> check of the device.
> fsck exited with status code 8
> done.
> Warning: File system check failed but did not detect errors
> 
> and then I get login prompt.
> 
> 
> With reverted fffb6e12233002c26c0ee9ff92fa87927cd779f2, virtio-vscsi behaves
> the same (so I assume fffb6e122 does not affect it) and ibm-vscsi behaves nicely:
> 
> Begin: Loading essential drivers ... done.
> Begin: Running /scripts/init-premount ... done.
> Begin: Mounting root file system ... Begin: Running /scripts/local-top ... done.
> Begin: Running /scripts/local-premount ... done.
> Begin: Will now check root file system ... fsck from util-linux 2.27.1
> [/sbin/fsck.ext4 (1) -- /dev/sda2] fsck.ext4 -a -C0 /dev/sda2
> /dev/sda2: clean, 66846/2011296 files, 574929/8034048 blocks
> done.
> [    0.996954] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts: (null)
> done.
> 
> and then I get login prompt.
> 
> 
> fffb6e12233002c26c0ee9ff92fa87927cd779f2 is:
> ===
> block: use aio_bh_schedule_oneshot
> 
> This simplifies bottom half handlers by removing calls to qemu_bh_delete and
> thus removing the need to stash the bottom half pointer in the opaque
> datum.
> ===
> 
> Any clues what is wrong? Thanks.

Hi, it turns out that the fix is already included in the 20-patch
series "dataplane: remove RFifoLock".  It's in patch 17.


diff --git a/async.c b/async.c
index f30d011..fb37b03 100644
--- a/async.c
+++ b/async.c
@@ -61,6 +61,7 @@ void aio_bh_schedule_oneshot(AioContext *ctx, QEMUBHFunc *cb, void *opaque)
     smp_wmb();
     ctx->first_bh = bh;
     qemu_mutex_unlock(&ctx->bh_lock);
+    aio_notify(ctx);
 }
 
 QEMUBH *aio_bh_new(AioContext *ctx, QEMUBHFunc *cb, void *opaque)

Thanks,

Paolo