cros_async: Don't use io_uring on kernels < 5.10

Kernels before 5.10 had known bugs in the io_uring implementation.
Don't use io_uring when we detect this.  Also skip all the io_uring
tests in this case.

BUG=none
TEST=cargo test

Change-Id: I5fd6203ad25a6fb85ff28f1a6ddb0181f836ad89
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3006309
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Chirantan Ekbote <chirantan@chromium.org>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-by: Woody Chow <woodychow@google.com>

Cargo.lock

@@ -194,6 +194,7 @@ dependencies = [
  "intrusive-collections",
  "io_uring",
  "libc",
+ "once_cell",
  "paste",
  "pin-utils",
  "slab",

cros_async/Cargo.toml

@@ -7,15 +7,16 @@ edition = "2018"
 [dependencies]
 async-trait = "0.1.36"
 async-task = "4"
+data_model = { path = "../data_model" } # provided by ebuild
 intrusive-collections = "0.9"
 io_uring = { path = "../io_uring" } # provided by ebuild
 libc = "*"
+once_cell = "1.7.2"
 paste = "1.0"
 pin-utils = "0.1.0-alpha.4"
 slab = "0.4"
 sync = { path = "../sync" } # provided by ebuild
 sys_util = { path = "../sys_util" } # provided by ebuild
-data_model = { path = "../data_model" } # provided by ebuild
 thiserror = "1.0.20"
 
 [dependencies.futures]

cros_async/src/uring_executor.rs

@@ -52,13 +52,14 @@
 //! ensure it lives long enough.
 
 use std::convert::TryInto;
+use std::ffi::CStr;
 use std::fs::File;
 use std::future::Future;
 use std::io;
-use std::mem;
+use std::mem::{self, MaybeUninit};
 use std::os::unix::io::{AsRawFd, FromRawFd, RawFd};
 use std::pin::Pin;
-use std::sync::atomic::{AtomicI32, AtomicU32, Ordering};
+use std::sync::atomic::{AtomicI32, Ordering};
 use std::sync::{Arc, Weak};
 use std::task::Waker;
 use std::task::{Context, Poll};
@@ -67,6 +68,7 @@ use std::thread::{self, ThreadId};
 use async_task::Task;
 use futures::task::noop_waker;
 use io_uring::URingContext;
+use once_cell::sync::Lazy;
 use pin_utils::pin_mut;
 use slab::Slab;
 use sync::Mutex;
@@ -130,29 +132,41 @@ impl From<Error> for io::Error {
     }
 }
 
+static USE_URING: Lazy<bool> = Lazy::new(|| {
+    let mut utsname = MaybeUninit::zeroed();
+
+    // Safe because this will only modify `utsname` and we check the return value.
+    let res = unsafe { libc::uname(utsname.as_mut_ptr()) };
+    if res < 0 {
+        return false;
+    }
+
+    // Safe because the kernel has initialized `utsname`.
+    let utsname = unsafe { utsname.assume_init() };
+
+    // Safe because the pointer is valid and the kernel guarantees that this is a valid C string.
+    let release = unsafe { CStr::from_ptr(utsname.release.as_ptr()) };
+
+    let mut components = match release.to_str().map(|r| r.split('.').map(str::parse)) {
+        Ok(c) => c,
+        Err(_) => return false,
+    };
+
+    // Kernels older than 5.10 either didn't support io_uring or had bugs in the implementation.
+    match (components.next(), components.next()) {
+        (Some(Ok(major)), Some(Ok(minor))) if (major, minor) >= (5, 10) => {
+            // The kernel version is new enough so check if we can actually make a uring context.
+            URingContext::new(8).is_ok()
+        }
+        _ => false,
+    }
+});
+
 // Checks if the uring executor is available.
 // Caches the result so that the check is only run once.
 // Useful for falling back to the FD executor on pre-uring kernels.
 pub(crate) fn use_uring() -> bool {
-    const UNKNOWN: u32 = 0;
-    const URING: u32 = 1;
-    const FD: u32 = 2;
-    static USE_URING: AtomicU32 = AtomicU32::new(UNKNOWN);
-    match USE_URING.load(Ordering::Relaxed) {
-        UNKNOWN => {
-            // Create a dummy uring context to check that the kernel understands the syscalls.
-            if URingContext::new(8).is_ok() {
-                USE_URING.store(URING, Ordering::Relaxed);
-                true
-            } else {
-                USE_URING.store(FD, Ordering::Relaxed);
-                false
-            }
-        }
-        URING => true,
-        FD => false,
-        _ => unreachable!("invalid use uring state"),
-    }
+    *USE_URING
 }
 
 pub struct RegisteredSource {
@@ -880,6 +894,10 @@ mod tests {
 
     #[test]
     fn dont_drop_backing_mem_read() {
+        if !use_uring() {
+            return;
+        }
+
         // Create a backing memory wrapped in an Arc and check that the drop isn't called while the
         // op is pending.
         let bm =
@@ -920,6 +938,10 @@ mod tests {
 
     #[test]
     fn dont_drop_backing_mem_write() {
+        if !use_uring() {
+            return;
+        }
+
         // Create a backing memory wrapped in an Arc and check that the drop isn't called while the
         // op is pending.
         let bm =
@@ -961,6 +983,10 @@ mod tests {
 
     #[test]
     fn canceled_before_completion() {
+        if !use_uring() {
+            return;
+        }
+
         async fn cancel_io(op: PendingOperation) {
             mem::drop(op);
         }
@@ -999,6 +1025,10 @@ mod tests {
 
     #[test]
     fn drop_before_completion() {
+        if !use_uring() {
+            return;
+        }
+
         const VALUE: u64 = 0xef6c_a8df_b842_eb9c;
 
         async fn check_op(op: PendingOperation) {
@@ -1044,6 +1074,10 @@ mod tests {
 
     #[test]
     fn drop_on_different_thread() {
+        if !use_uring() {
+            return;
+        }
+
         let ex = URingExecutor::new().unwrap();
 
         let ex2 = ex.clone();

cros_async/src/uring_source.rs

@@ -18,26 +18,6 @@ use crate::AsyncResult;
 /// `UringSource` wraps FD backed IO sources for use with io_uring. It is a thin wrapper around
 /// registering an IO source with the uring that provides an `IoSource` implementation.
 /// Most useful functions are provided by 'IoSourceExt'.
-///
-/// # Example
-/// ```rust
-/// use std::fs::File;
-/// use cros_async::{UringSource, ReadAsync, URingExecutor};
-///
-/// async fn read_four_bytes(source: &UringSource<File>) -> (usize, Vec<u8>) {
-///    let mem = vec![0u8; 4];
-///    source.read_to_vec(0, mem).await.unwrap()
-/// }
-///
-/// fn read_file(f: File) -> Result<(), Box<dyn std::error::Error>> {
-///     let ex = URingExecutor::new()?;
-///     let async_source = UringSource::new(f, &ex)?;
-///     let (nread, vec) = ex.run_until(read_four_bytes(&async_source))?;
-///     assert_eq!(nread, 4);
-///     assert_eq!(vec.len(), 4);
-///     Ok(())
-/// }
-/// ```
 pub struct UringSource<F: AsRawFd> {
     registered_source: RegisteredSource,
     source: F,
@@ -236,12 +216,17 @@ mod tests {
     use std::path::PathBuf;
 
     use crate::io_ext::{ReadAsync, WriteAsync};
+    use crate::uring_executor::use_uring;
     use crate::UringSource;
 
     use super::*;
 
     #[test]
     fn read_to_mem() {
+        if !use_uring() {
+            return;
+        }
+
         use crate::mem::VecIoWrapper;
         use std::io::Write;
         use tempfile::tempfile;
@@ -275,6 +260,10 @@ mod tests {
 
     #[test]
     fn readvec() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = File::open("/dev/zero").unwrap();
             let source = UringSource::new(f, ex).unwrap();
@@ -293,6 +282,10 @@ mod tests {
 
     #[test]
     fn readmulti() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = File::open("/dev/zero").unwrap();
             let source = UringSource::new(f, ex).unwrap();
@@ -321,6 +314,10 @@ mod tests {
 
     #[test]
     fn u64_from_file() {
+        if !use_uring() {
+            return;
+        }
+
         let f = File::open("/dev/zero").unwrap();
         let ex = URingExecutor::new().unwrap();
         let source = UringSource::new(f, &ex).unwrap();
@@ -330,6 +327,10 @@ mod tests {
 
     #[test]
     fn event() {
+        if !use_uring() {
+            return;
+        }
+
         use sys_util::EventFd;
 
         async fn write_event(ev: EventFd, wait: EventFd, ex: &URingExecutor) {
@@ -367,6 +368,10 @@ mod tests {
 
     #[test]
     fn pend_on_pipe() {
+        if !use_uring() {
+            return;
+        }
+
         use std::io::Write;
 
         use futures::future::Either;
@@ -393,6 +398,10 @@ mod tests {
 
     #[test]
     fn readmem() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = File::open("/dev/zero").unwrap();
             let source = UringSource::new(f, ex).unwrap();
@@ -443,6 +452,10 @@ mod tests {
 
     #[test]
     fn range_error() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = File::open("/dev/zero").unwrap();
             let source = UringSource::new(f, ex).unwrap();
@@ -467,6 +480,10 @@ mod tests {
 
     #[test]
     fn fallocate() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let dir = tempfile::TempDir::new().unwrap();
             let mut file_path = PathBuf::from(dir.path());
@@ -500,6 +517,10 @@ mod tests {
 
     #[test]
     fn fsync() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = tempfile::tempfile().unwrap();
             let source = UringSource::new(f, ex).unwrap();
@@ -512,6 +533,10 @@ mod tests {
 
     #[test]
     fn wait_read() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = File::open("/dev/zero").unwrap();
             let source = UringSource::new(f, ex).unwrap();
@@ -524,6 +549,10 @@ mod tests {
 
     #[test]
     fn writemem() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = OpenOptions::new()
                 .create(true)
@@ -546,6 +575,10 @@ mod tests {
 
     #[test]
     fn writevec() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = OpenOptions::new()
                 .create(true)
@@ -567,6 +600,10 @@ mod tests {
 
     #[test]
     fn writemulti() {
+        if !use_uring() {
+            return;
+        }
+
         async fn go(ex: &URingExecutor) {
             let f = OpenOptions::new()
                 .create(true)

seccomp/aarch64/common_device.policy

@@ -44,3 +44,4 @@ sigaltstack: 1
 write: 1
 writev: 1
 fcntl: 1
+uname: 1

seccomp/aarch64/gpu_device.policy

@@ -42,6 +42,7 @@ set_robust_list: 1
 sigaltstack: 1
 write: 1
 writev: 1
+uname: 1
 
 # Required for perfetto tracing
 getsockopt: 1
@@ -77,7 +78,6 @@ tgkill: 1
 clock_gettime: 1
 
 # Rules specific to Mesa.
-uname: 1
 sched_setscheduler: 1
 sched_setaffinity: 1
 kcmp: 1

seccomp/aarch64/xhci.policy

@@ -17,7 +17,6 @@ openat: 1
 setsockopt: 1
 bind: 1
 socket: arg0 == AF_NETLINK
-uname: 1
 # The following ioctls are:
 # 0x4004550d == USBDEVFS_REAPURBNDELAY32
 # 0x550b     == USBDEVFS_DISCARDURB

seccomp/arm/common_device.policy

@@ -53,3 +53,4 @@ sigaltstack: 1
 write: 1
 writev: 1
 fcntl64: 1
+uname: 1

seccomp/arm/gpu_device.policy

@@ -48,6 +48,7 @@ set_robust_list: 1
 sigaltstack: 1
 write: 1
 writev: 1
+uname: 1
 
 # Required for perfetto tracing
 getsockopt: 1
@@ -89,7 +90,6 @@ clock_gettime: 1
 clock_gettime64: 1
 
 # Rules specific to Mesa.
-uname: 1
 sched_setscheduler: 1
 sched_setaffinity: 1
 kcmp: 1

seccomp/arm/xhci.policy

@@ -19,7 +19,6 @@ bind: 1
 socket: arg0 == AF_NETLINK
 stat: 1
 statx: 1
-uname: 1
 # The following ioctls are:
 # 0x4004550d == USBDEVFS_REAPURBNDELAY32
 # 0x550b     == USBDEVFS_DISCARDURB

seccomp/x86_64/common_device.policy

@@ -47,3 +47,4 @@ sigaltstack: 1
 write: 1
 writev: 1
 fcntl: 1
+uname: 1

seccomp/x86_64/gpu_device.policy

@@ -45,6 +45,7 @@ set_robust_list: 1
 sigaltstack: 1
 write: 1
 writev: 1
+uname: 1
 
 # Rules specific to gpu
 connect: 1
@@ -90,7 +91,6 @@ setpriority: 1
 unlink: 1
 
 # Rules specific to AMD gpus.
-uname: 1
 sched_setscheduler: 1
 sched_setaffinity: 1
 kcmp: 1

seccomp/x86_64/video_device.policy

@@ -35,7 +35,6 @@ mprotect: arg2 == PROT_READ|PROT_WRITE || arg2 == PROT_NONE || arg2 == PROT_READ
 readlink: 1
 sched_setaffinity: 1
 sched_setscheduler: arg1 == SCHED_IDLE || arg1 == SCHED_BATCH
-uname: 1
 
 # Required by mesa on AMD GPU
 sysinfo: 1

seccomp/x86_64/xhci.policy

@@ -18,7 +18,6 @@ open: return ENOENT
 openat: 1
 socket: arg0 == AF_NETLINK
 stat: 1
-uname: 1
 # The following ioctls are:
 # 0x4008550d == USBDEVFS_REAPURBNDELAY
 # 0x41045508 == USBDEVFS_GETDRIVER