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devices: virtio: block: disable EVENT_IDX feature

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This disables the VIRTIO_RING_F_EVENT_IDX optimization, which seems to
be causing I/O to sometimes not complete when used with the Linux virtio
block guest driver.  The exact root cause is not clear (possibly a
race/memory ordering issue when reading and updating the event index),
but disabling the feature flag is enough to get back to a reliable state
while the failure is debugged.

The particular test case that triggers this typically reproduces as a
hung task in btrfs waiting for an I/O completion that never shows up.
With the EVENT_IDX feature disabled, I am not able to reproduce the hang
after many hours of running the test case.

BUG=chromium:1097385
TEST=Run reproducer test case; do not observe any hung tasks

Change-Id: Iaf37722f23c05276ec65f4d4a10c4a47af764538
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2486671
Reviewed-by: Dylan Reid <dgreid@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>
This commit is contained in:
Daniel Verkamp 2020-10-20 00:07:49 -07:00 committed by Commit Bot
parent 7d2b8ac342
commit 4a401cce0c
1 changed files with 5 additions and 8 deletions
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13
devices/src/virtio/block.rs
View file

@ -20,7 +20,6 @@ use data_model::{DataInit, Le16, Le32, Le64};
use disk::DiskFile;
use msg_socket::{MsgReceiver, MsgSender};
use sync::Mutex;
use virtio_sys::virtio_ring::VIRTIO_RING_F_EVENT_IDX;
use vm_control::{DiskControlCommand, DiskControlResponseSocket, DiskControlResult};
use vm_memory::GuestMemory;
@ -529,7 +528,6 @@ impl Block {
let mut avail_features: u64 = base_features;
avail_features |= 1 << VIRTIO_BLK_F_FLUSH;
avail_features |= 1 << VIRTIO_RING_F_EVENT_IDX;
if read_only {
avail_features |= 1 << VIRTIO_BLK_F_RO;
} else {
@ -882,8 +880,8 @@ mod tests {
let b = Block::new(features, Box::new(f), false, true, 512, None).unwrap();
// writable device should set VIRTIO_BLK_F_FLUSH + VIRTIO_BLK_F_DISCARD
// + VIRTIO_BLK_F_WRITE_ZEROES + VIRTIO_F_VERSION_1 + VIRTIO_BLK_F_BLK_SIZE
// + VIRTIO_BLK_F_SEG_MAX + VIRTIO_RING_F_EVENT_IDX
assert_eq!(0x120006244, b.features());
// + VIRTIO_BLK_F_SEG_MAX
assert_eq!(0x100006244, b.features());
}
// read-write block device, non-sparse
@ -893,8 +891,8 @@ mod tests {
let b = Block::new(features, Box::new(f), false, false, 512, None).unwrap();
// writable device should set VIRTIO_BLK_F_FLUSH
// + VIRTIO_BLK_F_WRITE_ZEROES + VIRTIO_F_VERSION_1 + VIRTIO_BLK_F_BLK_SIZE
// + VIRTIO_BLK_F_SEG_MAX + VIRTIO_RING_F_EVENT_IDX
assert_eq!(0x120004244, b.features());
// + VIRTIO_BLK_F_SEG_MAX
assert_eq!(0x100004244, b.features());
}
// read-only block device
@ -904,8 +902,7 @@ mod tests {
let b = Block::new(features, Box::new(f), true, true, 512, None).unwrap();
// read-only device should set VIRTIO_BLK_F_FLUSH and VIRTIO_BLK_F_RO
// + VIRTIO_F_VERSION_1 + VIRTIO_BLK_F_BLK_SIZE + VIRTIO_BLK_F_SEG_MAX
// + VIRTIO_RING_F_EVENT_IDX
assert_eq!(0x120000264, b.features());
assert_eq!(0x100000264, b.features());
}
}