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Fix block device resize disk #7948

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Merged
rbradford merged 2 commits into from
Apr 17, 2026
+33 −5
Merged

Fix block device resize disk #7948

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fc94e6a
virtio-devices: Make pause idempotent to prevent deadlock
vincent-thomas Apr 9, 2026
e91273d
block: Fix resize for block device backends
vincent-thomas Apr 9, 2026
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30 changes: 26 additions & 4 deletions block/src/raw_async.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -3,7 +3,8 @@
// SPDX-License-Identifier: Apache-2.0 AND BSD-3-Clause

use std::fs::File;
use std::io::Error;
use std::io::{self, Error};
use std::os::unix::fs::FileTypeExt;
use std::os::unix::io::{AsRawFd, RawFd};

use io_uring::{IoUring, opcode, types};
Expand Down Expand Up @@ -68,9 +69,30 @@ impl disk_file::SparseCapable for RawFileDisk {

impl disk_file::Resizable for RawFileDisk {
fn resize(&mut self, size: u64) -> BlockResult<()> {
self.file
.set_len(size)
.map_err(|e| BlockError::new(BlockErrorKind::Io, DiskFileError::ResizeError(e)))
let fd_metadata = self
.file
.metadata()
.map_err(|e| BlockError::new(BlockErrorKind::Io, DiskFileError::ResizeError(e)))?;

if fd_metadata.file_type().is_block_device() {
// Block devices cannot be resized via ftruncate - they are resized
// externally (LVM, losetup -c, etc.). Verify the size matches.
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let (actual_size, _) = query_device_size(&self.file)
.map_err(|e| BlockError::new(BlockErrorKind::Io, DiskFileError::ResizeError(e)))?;
if actual_size != size {
return Err(BlockError::new(
BlockErrorKind::Io,
DiskFileError::ResizeError(io::Error::other(format!(
"Block device size {actual_size} does not match requested size {size}"
))),
));
}
Ok(())
} else {
self.file
.set_len(size)
.map_err(|e| BlockError::new(BlockErrorKind::Io, DiskFileError::ResizeError(e)))
}
}
}

Expand Down
8 changes: 7 additions & 1 deletion virtio-devices/src/device.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -340,7 +340,13 @@ impl Pausable for VirtioCommon {
"Pausing virtio-{}",
VirtioDeviceType::from(self.device_type)
);
self.paused.store(true, Ordering::SeqCst);

// If already paused, return early to avoid deadlock waiting on barrier
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@phip1611 phip1611 Apr 10, 2026

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This situation occurs when the VMM thread holds a device mutex while
calling an operation that triggers pause(), and a vCPU thread
simultaneously needs that same mutex for MMIO access. With slow I/O
backends (like RBD/Ceph), the timing window for this race is larger,
making the deadlock more likely to occur.

Ah, wait. Doesn't this open another race window? Another thread may unpause this too early? Or are we protected by mutexes?

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@rbradford rbradford Apr 16, 2026

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Maybe this is another place where we need a three-way handshake with atomic

RUNNING -> PAUSING -> PAUSED

It might not strictly needed in this case since we don't really do anything after.

// for worker threads that are already parked.
if self.paused.swap(true, Ordering::SeqCst) {
return Ok(());
}

if let Some(pause_evt) = &self.pause_evt {
pause_evt
.write(1)
Expand Down
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