rust: upgrade to Rust 1.72.1

This is the third upgrade to the Rust toolchain, from 1.71.1 to 1.72.1
(i.e. the latest) [1].

See the upgrade policy [2] and the comments on the first upgrade in
commit 3ed03f4da06e ("rust: upgrade to Rust 1.68.2").

# Unstable features

No unstable features (that we use) were stabilized.

Therefore, the only unstable feature allowed to be used outside
the `kernel` crate is still `new_uninit`, though other code to be
upstreamed may increase the list.

Please see [3] for details.

# Other improvements

Previously, the compiler could incorrectly generate a `.eh_frame`
section under `-Cpanic=abort`. We were hitting this bug when debug
assertions were enabled (`CONFIG_RUST_DEBUG_ASSERTIONS=y`) [4]:

      LD      .tmp_vmlinux.kallsyms1
    ld.lld: error: <internal>:(.eh_frame) is being placed in '.eh_frame'

Gary fixed the issue in Rust 1.72.0 [5].

# Required changes

For the upgrade, the following changes are required:

  - A call to `Box::from_raw` in `rust/kernel/sync/arc.rs` now requires
    an explicit `drop()` call. See previous patch for details.

# `alloc` upgrade and reviewing

The vast majority of changes are due to our `alloc` fork being upgraded
at once.

There are two kinds of changes to be aware of: the ones coming from
upstream, which we should follow as closely as possible, and the updates
needed in our added fallible APIs to keep them matching the newer
infallible APIs coming from upstream.

Instead of taking a look at the diff of this patch, an alternative
approach is reviewing a diff of the changes between upstream `alloc` and
the kernel's. This allows to easily inspect the kernel additions only,
especially to check if the fallible methods we already have still match
the infallible ones in the new version coming from upstream.

Another approach is reviewing the changes introduced in the additions in
the kernel fork between the two versions. This is useful to spot
potentially unintended changes to our additions.

To apply these approaches, one may follow steps similar to the following
to generate a pair of patches that show the differences between upstream
Rust and the kernel (for the subset of `alloc` we use) before and after
applying this patch:

    # Get the difference with respect to the old version.
    git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
    git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
        cut -d/ -f3- |
        grep -Fv README.md |
        xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
    git -C linux diff --patch-with-stat --summary -R > old.patch
    git -C linux restore rust/alloc

    # Apply this patch.
    git -C linux am rust-upgrade.patch

    # Get the difference with respect to the new version.
    git -C rust checkout $(linux/scripts/min-tool-version.sh rustc)
    git -C linux ls-tree -r --name-only HEAD -- rust/alloc |
        cut -d/ -f3- |
        grep -Fv README.md |
        xargs -IPATH cp rust/library/alloc/src/PATH linux/rust/alloc/PATH
    git -C linux diff --patch-with-stat --summary -R > new.patch
    git -C linux restore rust/alloc

Now one may check the `new.patch` to take a look at the additions (first
approach) or at the difference between those two patches (second
approach). For the latter, a side-by-side tool is recommended.

Link: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1721-2023-09-19 [1]
Link: https://rust-for-linux.com/rust-version-policy [2]
Link: https://github.com/Rust-for-Linux/linux/issues/2 [3]
Closes: https://github.com/Rust-for-Linux/linux/issues/1012 [4]
Link: https://github.com/rust-lang/rust/pull/112403 [5]
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Link: https://lore.kernel.org/r/20230823160244.188033-3-ojeda@kernel.org
[ Used 1.72.1 instead of .0 (no changes in `alloc`) and reworded
  to mention that we hit the `.eh_frame` bug under debug assertions. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 51 insertions, 55 deletions

diff --git a/rust/alloc/vec/mod.rs b/rust/alloc/vec/mod.rs
index 05c70de0227e..a4e9a5002a6d 100644
--- a/rust/alloc/vec/mod.rs
+++ b/rust/alloc/vec/mod.rs
@@ -74,10 +74,10 @@ use crate::boxed::Box;
 use crate::collections::{TryReserveError, TryReserveErrorKind};
 use crate::raw_vec::RawVec;
 
-#[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-pub use self::drain_filter::DrainFilter;
+#[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
+pub use self::extract_if::ExtractIf;
 
-mod drain_filter;
+mod extract_if;
 
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "vec_splice", since = "1.21.0")]
@@ -618,22 +618,20 @@ impl<T> Vec<T> {
     /// Using memory that was allocated elsewhere:
     ///
     /// ```rust
-    /// #![feature(allocator_api)]
-    ///
-    /// use std::alloc::{AllocError, Allocator, Global, Layout};
+    /// use std::alloc::{alloc, Layout};
     ///
     /// fn main() {
     ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
     ///
     ///     let vec = unsafe {
-    ///         let mem = match Global.allocate(layout) {
-    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
-    ///             Err(AllocError) => return,
-    ///         };
+    ///         let mem = alloc(layout).cast::<u32>();
+    ///         if mem.is_null() {
+    ///             return;
+    ///         }
     ///
     ///         mem.write(1_000_000);
     ///
-    ///         Vec::from_raw_parts_in(mem, 1, 16, Global)
+    ///         Vec::from_raw_parts(mem, 1, 16)
     ///     };
     ///
     ///     assert_eq!(vec, &[1_000_000]);
@@ -876,19 +874,22 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Using memory that was allocated elsewhere:
     ///
     /// ```rust
-    /// use std::alloc::{alloc, Layout};
+    /// #![feature(allocator_api)]
+    ///
+    /// use std::alloc::{AllocError, Allocator, Global, Layout};
     ///
     /// fn main() {
     ///     let layout = Layout::array::<u32>(16).expect("overflow cannot happen");
+    ///
     ///     let vec = unsafe {
-    ///         let mem = alloc(layout).cast::<u32>();
-    ///         if mem.is_null() {
-    ///             return;
-    ///         }
+    ///         let mem = match Global.allocate(layout) {
+    ///             Ok(mem) => mem.cast::<u32>().as_ptr(),
+    ///             Err(AllocError) => return,
+    ///         };
     ///
     ///         mem.write(1_000_000);
     ///
-    ///         Vec::from_raw_parts(mem, 1, 16)
+    ///         Vec::from_raw_parts_in(mem, 1, 16, Global)
     ///     };
     ///
     ///     assert_eq!(vec, &[1_000_000]);
@@ -2507,7 +2508,7 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
         let len = self.len();
 
         if new_len > len {
-            self.extend_with(new_len - len, ExtendElement(value))
+            self.extend_with(new_len - len, value)
         } else {
             self.truncate(new_len);
         }
@@ -2545,7 +2546,7 @@ impl<T: Clone, A: Allocator> Vec<T, A> {
         let len = self.len();
 
         if new_len > len {
-            self.try_extend_with(new_len - len, ExtendElement(value))
+            self.try_extend_with(new_len - len, value)
         } else {
             self.truncate(new_len);
             Ok(())
@@ -2684,26 +2685,10 @@ impl<T, A: Allocator, const N: usize> Vec<[T; N], A> {
     }
 }
 
-// This code generalizes `extend_with_{element,default}`.
-trait ExtendWith<T> {
-    fn next(&mut self) -> T;
-    fn last(self) -> T;
-}
-
-struct ExtendElement<T>(T);
-impl<T: Clone> ExtendWith<T> for ExtendElement<T> {
-    fn next(&mut self) -> T {
-        self.0.clone()
-    }
-    fn last(self) -> T {
-        self.0
-    }
-}
-
-impl<T, A: Allocator> Vec<T, A> {
+impl<T: Clone, A: Allocator> Vec<T, A> {
     #[cfg(not(no_global_oom_handling))]
-    /// Extend the vector by `n` values, using the given generator.
-    fn extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) {
+    /// Extend the vector by `n` clones of value.
+    fn extend_with(&mut self, n: usize, value: T) {
         self.reserve(n);
 
         unsafe {
@@ -2715,15 +2700,15 @@ impl<T, A: Allocator> Vec<T, A> {
 
             // Write all elements except the last one
             for _ in 1..n {
-                ptr::write(ptr, value.next());
+                ptr::write(ptr, value.clone());
                 ptr = ptr.add(1);
-                // Increment the length in every step in case next() panics
+                // Increment the length in every step in case clone() panics
                 local_len.increment_len(1);
             }
 
             if n > 0 {
                 // We can write the last element directly without cloning needlessly
-                ptr::write(ptr, value.last());
+                ptr::write(ptr, value);
                 local_len.increment_len(1);
             }
 
@@ -2731,8 +2716,8 @@ impl<T, A: Allocator> Vec<T, A> {
         }
     }
 
-    /// Try to extend the vector by `n` values, using the given generator.
-    fn try_extend_with<E: ExtendWith<T>>(&mut self, n: usize, mut value: E) -> Result<(), TryReserveError> {
+    /// Try to extend the vector by `n` clones of value.
+    fn try_extend_with(&mut self, n: usize, value: T) -> Result<(), TryReserveError> {
         self.try_reserve(n)?;
 
         unsafe {
@@ -2744,15 +2729,15 @@ impl<T, A: Allocator> Vec<T, A> {
 
             // Write all elements except the last one
             for _ in 1..n {
-                ptr::write(ptr, value.next());
+                ptr::write(ptr, value.clone());
                 ptr = ptr.add(1);
-                // Increment the length in every step in case next() panics
+                // Increment the length in every step in case clone() panics
                 local_len.increment_len(1);
             }
 
             if n > 0 {
                 // We can write the last element directly without cloning needlessly
-                ptr::write(ptr, value.last());
+                ptr::write(ptr, value);
                 local_len.increment_len(1);
             }
 
@@ -3210,6 +3195,12 @@ impl<T, A: Allocator> Vec<T, A> {
     /// If the closure returns false, the element will remain in the vector and will not be yielded
     /// by the iterator.
     ///
+    /// If the returned `ExtractIf` is not exhausted, e.g. because it is dropped without iterating
+    /// or the iteration short-circuits, then the remaining elements will be retained.
+    /// Use [`retain`] with a negated predicate if you do not need the returned iterator.
+    ///
+    /// [`retain`]: Vec::retain
+    ///
     /// Using this method is equivalent to the following code:
     ///
     /// ```
@@ -3228,10 +3219,10 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # assert_eq!(vec, vec![1, 4, 5]);
     /// ```
     ///
-    /// But `drain_filter` is easier to use. `drain_filter` is also more efficient,
+    /// But `extract_if` is easier to use. `extract_if` is also more efficient,
     /// because it can backshift the elements of the array in bulk.
     ///
-    /// Note that `drain_filter` also lets you mutate every element in the filter closure,
+    /// Note that `extract_if` also lets you mutate every element in the filter closure,
     /// regardless of whether you choose to keep or remove it.
     ///
     /// # Examples
@@ -3239,17 +3230,17 @@ impl<T, A: Allocator> Vec<T, A> {
     /// Splitting an array into evens and odds, reusing the original allocation:
     ///
     /// ```
-    /// #![feature(drain_filter)]
+    /// #![feature(extract_if)]
     /// let mut numbers = vec![1, 2, 3, 4, 5, 6, 8, 9, 11, 13, 14, 15];
     ///
-    /// let evens = numbers.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
+    /// let evens = numbers.extract_if(|x| *x % 2 == 0).collect::<Vec<_>>();
     /// let odds = numbers;
     ///
     /// assert_eq!(evens, vec![2, 4, 6, 8, 14]);
     /// assert_eq!(odds, vec![1, 3, 5, 9, 11, 13, 15]);
     /// ```
-    #[unstable(feature = "drain_filter", reason = "recently added", issue = "43244")]
-    pub fn drain_filter<F>(&mut self, filter: F) -> DrainFilter<'_, T, F, A>
+    #[unstable(feature = "extract_if", reason = "recently added", issue = "43244")]
+    pub fn extract_if<F>(&mut self, filter: F) -> ExtractIf<'_, T, F, A>
     where
         F: FnMut(&mut T) -> bool,
     {
@@ -3260,7 +3251,7 @@ impl<T, A: Allocator> Vec<T, A> {
             self.set_len(0);
         }
 
-        DrainFilter { vec: self, idx: 0, del: 0, old_len, pred: filter, panic_flag: false }
+        ExtractIf { vec: self, idx: 0, del: 0, old_len, pred: filter }
     }
 }
 
@@ -3290,9 +3281,14 @@ impl<'a, T: Copy + 'a, A: Allocator + 'a> Extend<&'a T> for Vec<T, A> {
 
 /// Implements comparison of vectors, [lexicographically](Ord#lexicographical-comparison).
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: PartialOrd, A: Allocator> PartialOrd for Vec<T, A> {
+impl<T, A1, A2> PartialOrd<Vec<T, A2>> for Vec<T, A1>
+where
+    T: PartialOrd,
+    A1: Allocator,
+    A2: Allocator,
+{
     #[inline]
-    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+    fn partial_cmp(&self, other: &Vec<T, A2>) -> Option<Ordering> {
         PartialOrd::partial_cmp(&**self, &**other)
     }
 }