Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-tracegrafted

Pull tracing fixes from Steven Rostedt:

 - Fix error output of boot instance creation failure

   Currently if a boot instance creation fails, instead of printing out
   the name of the instance that failed, it prints "(null)". That is
   because it prints "cur_str" that had already been processed by
   strsep(). Print the saved name instead.

   While at it, print the error code of the failure.

 - Fix use-after-free for same named historgrams

   Histograms can be named so that they can be used in multiple events.
   But if the named histogram has a variable attached, the second event
   that uses the named histogram which duplicates it and needs to free
   the original after duplication leaves the old variable in place and
   still visible. If another histogram uses than variable, it will use
   the stale one which will try to reference the freed duplicate
   histogram and crash the kernel.

   Free the duplicate variables along with the duplicated histogram
   data.

 - Check return value of kthread_run() in event self test

   The events self tests uses a kthread for testing but does not check
   if it succeeded in creating a kthread. If the kthread creation were
   to fail, the code will still try to call kthread_stop() on the error
   returned.

 - Fix race between reading trace_pipe and updating subbuffer size

   If a user is reading the trace_pipe file at the same time they update
   the ring buffer sub-buffer size, can cause the trace_pipe read to
   read stale data. Add trace_access_lock() around updating the ring
   buffer sub-buffer size.

 - Fix eventfs_inode on failure path in creation of the events directory

   In the creation of the "events" directory, if after allocating the
   eventfs_inode a failure is detected, it calls cleanup_ei() which
   calls free_ei(). The free_ei() will test if eventfs_inode being freed
   has no children. It is a bug if it does. But on the failure case of
   the creation of the "events" directory, the children lists have not
   yet been initialized and the free will trigger a warning because
   list_empty() on an uninitialized list returns false.

   Move the initialization into init_ei() where it makes more sense and
   makes sure that a created eventfs_inode has its lists initialized
   upon creation.

 - Check return value of kthread_run() in ftrace direct sample code

   The sample code that shows how to use the ftrace direct calls does
   not test the return of kthread_run() to see if it succeeds. Return a
   failure if the kthread_run() doesn't succeed.

 - Clear user events state on fork in case of alloc failure

   On fork, the child gets a pointer to the parent's user events state.
   It makes a copy of it then updates the child's pointer to it. But if
   the allocation fails, the duplication function leaves the child with
   a pointer to its parent's descriptor. When the child cleans up its
   data, it will free the parent's descriptor while the parent is still
   using it.

   In the duplication function, set the child's user_event_mm to NULL
   before testing if the allocation succeeded, and when it exits it will
   not free the parent's descriptor.

 - Fix retry exhaustion in simple ring buffer reader swap

   simple_ring_buffer_swap_reader_page() starts with retry set to 8 and
   post-decrements it only after a failed link replacement. On the final
   attempt, a successful replacement leaves retry at zero, while a
   failed replacement leaves it at -1.

   But the check for success expects the retry value to be non-zero and
   exits with an error on zero. This is the opposite result. Fix it.

 - Fail nicely when the remote swap_reader_page() returns an error

   Currently, if the swap_reader_page() of a remote buffer fails, it
   triggers a WARN_ON_ONCE() and continues normally. Instead, have it
   exit with an error and a pr_warn() print instead of a full WARNING.

* tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  ring-buffer: Stop remote reader update when page swap fails
  tracing: Fix retry exhaustion in simple ring buffer reader swap
  tracing/user_events: Clear copied tracing state before fork duplication
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-multi-modify
  samples/ftrace: Fix kthread_stop() on ERR_PTR in ftrace-direct-modify
  eventfs: Initialize ei->children and ei->list in init_ei()
  tracing: Fix use-after-free in trace_pipe read on sub-buffer order change
  tracing: Fix crash passing ERR_PTR to kthread_stop()
  tracing: Fix use-after-free with same-name named triggers
  tracing: Fix logged instance name on creation failure

1 files changed, 227 insertions, 0 deletions

diff --git a/rust/syn/discouraged.rs b/rust/syn/discouraged.rs
new file mode 100644
index 000000000..2acd631ec
--- /dev/null
+++ b/rust/syn/discouraged.rs
@@ -0,0 +1,227 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! Extensions to the parsing API with niche applicability.
+
+use crate::buffer::Cursor;
+use crate::error::Result;
+use crate::parse::{inner_unexpected, ParseBuffer, Unexpected};
+use proc_macro2::extra::DelimSpan;
+use proc_macro2::Delimiter;
+use std::cell::Cell;
+use std::mem;
+use std::rc::Rc;
+
+/// Extensions to the `ParseStream` API to support speculative parsing.
+pub trait Speculative {
+    /// Advance this parse stream to the position of a forked parse stream.
+    ///
+    /// This is the opposite operation to [`ParseStream::fork`]. You can fork a
+    /// parse stream, perform some speculative parsing, then join the original
+    /// stream to the fork to "commit" the parsing from the fork to the main
+    /// stream.
+    ///
+    /// If you can avoid doing this, you should, as it limits the ability to
+    /// generate useful errors. That said, it is often the only way to parse
+    /// syntax of the form `A* B*` for arbitrary syntax `A` and `B`. The problem
+    /// is that when the fork fails to parse an `A`, it's impossible to tell
+    /// whether that was because of a syntax error and the user meant to provide
+    /// an `A`, or that the `A`s are finished and it's time to start parsing
+    /// `B`s. Use with care.
+    ///
+    /// Also note that if `A` is a subset of `B`, `A* B*` can be parsed by
+    /// parsing `B*` and removing the leading members of `A` from the
+    /// repetition, bypassing the need to involve the downsides associated with
+    /// speculative parsing.
+    ///
+    /// [`ParseStream::fork`]: ParseBuffer::fork
+    ///
+    /// # Example
+    ///
+    /// There has been chatter about the possibility of making the colons in the
+    /// turbofish syntax like `path::to::<T>` no longer required by accepting
+    /// `path::to<T>` in expression position. Specifically, according to [RFC
+    /// 2544], [`PathSegment`] parsing should always try to consume a following
+    /// `<` token as the start of generic arguments, and reset to the `<` if
+    /// that fails (e.g. the token is acting as a less-than operator).
+    ///
+    /// This is the exact kind of parsing behavior which requires the "fork,
+    /// try, commit" behavior that [`ParseStream::fork`] discourages. With
+    /// `advance_to`, we can avoid having to parse the speculatively parsed
+    /// content a second time.
+    ///
+    /// This change in behavior can be implemented in syn by replacing just the
+    /// `Parse` implementation for `PathSegment`:
+    ///
+    /// ```
+    /// # use syn::ext::IdentExt;
+    /// use syn::parse::discouraged::Speculative;
+    /// # use syn::parse::{Parse, ParseStream};
+    /// # use syn::{Ident, PathArguments, Result, Token};
+    ///
+    /// pub struct PathSegment {
+    ///     pub ident: Ident,
+    ///     pub arguments: PathArguments,
+    /// }
+    /// #
+    /// # impl<T> From<T> for PathSegment
+    /// # where
+    /// #     T: Into<Ident>,
+    /// # {
+    /// #     fn from(ident: T) -> Self {
+    /// #         PathSegment {
+    /// #             ident: ident.into(),
+    /// #             arguments: PathArguments::None,
+    /// #         }
+    /// #     }
+    /// # }
+    ///
+    /// impl Parse for PathSegment {
+    ///     fn parse(input: ParseStream) -> Result<Self> {
+    ///         if input.peek(Token![super])
+    ///             || input.peek(Token![self])
+    ///             || input.peek(Token![Self])
+    ///             || input.peek(Token![crate])
+    ///         {
+    ///             let ident = input.call(Ident::parse_any)?;
+    ///             return Ok(PathSegment::from(ident));
+    ///         }
+    ///
+    ///         let ident = input.parse()?;
+    ///         if input.peek(Token![::]) && input.peek3(Token![<]) {
+    ///             return Ok(PathSegment {
+    ///                 ident,
+    ///                 arguments: PathArguments::AngleBracketed(input.parse()?),
+    ///             });
+    ///         }
+    ///         if input.peek(Token![<]) && !input.peek(Token![<=]) {
+    ///             let fork = input.fork();
+    ///             if let Ok(arguments) = fork.parse() {
+    ///                 input.advance_to(&fork);
+    ///                 return Ok(PathSegment {
+    ///                     ident,
+    ///                     arguments: PathArguments::AngleBracketed(arguments),
+    ///                 });
+    ///             }
+    ///         }
+    ///         Ok(PathSegment::from(ident))
+    ///     }
+    /// }
+    ///
+    /// # syn::parse_str::<PathSegment>("a<b,c>").unwrap();
+    /// ```
+    ///
+    /// # Drawbacks
+    ///
+    /// The main drawback of this style of speculative parsing is in error
+    /// presentation. Even if the lookahead is the "correct" parse, the error
+    /// that is shown is that of the "fallback" parse. To use the same example
+    /// as the turbofish above, take the following unfinished "turbofish":
+    ///
+    /// ```text
+    /// let _ = f<&'a fn(), for<'a> serde::>();
+    /// ```
+    ///
+    /// If this is parsed as generic arguments, we can provide the error message
+    ///
+    /// ```text
+    /// error: expected identifier
+    ///  --> src.rs:L:C
+    ///   |
+    /// L | let _ = f<&'a fn(), for<'a> serde::>();
+    ///   |                                    ^
+    /// ```
+    ///
+    /// but if parsed using the above speculative parsing, it falls back to
+    /// assuming that the `<` is a less-than when it fails to parse the generic
+    /// arguments, and tries to interpret the `&'a` as the start of a labelled
+    /// loop, resulting in the much less helpful error
+    ///
+    /// ```text
+    /// error: expected `:`
+    ///  --> src.rs:L:C
+    ///   |
+    /// L | let _ = f<&'a fn(), for<'a> serde::>();
+    ///   |               ^^
+    /// ```
+    ///
+    /// This can be mitigated with various heuristics (two examples: show both
+    /// forks' parse errors, or show the one that consumed more tokens), but
+    /// when you can control the grammar, sticking to something that can be
+    /// parsed LL(3) and without the LL(*) speculative parsing this makes
+    /// possible, displaying reasonable errors becomes much more simple.
+    ///
+    /// [RFC 2544]: https://github.com/rust-lang/rfcs/pull/2544
+    /// [`PathSegment`]: crate::PathSegment
+    ///
+    /// # Performance
+    ///
+    /// This method performs a cheap fixed amount of work that does not depend
+    /// on how far apart the two streams are positioned.
+    ///
+    /// # Panics
+    ///
+    /// The forked stream in the argument of `advance_to` must have been
+    /// obtained by forking `self`. Attempting to advance to any other stream
+    /// will cause a panic.
+    fn advance_to(&self, fork: &Self);
+}
+
+impl<'a> Speculative for ParseBuffer<'a> {
+    fn advance_to(&self, fork: &Self) {
+        if !crate::buffer::same_scope(self.cursor(), fork.cursor()) {
+            panic!("fork was not derived from the advancing parse stream");
+        }
+
+        let (self_unexp, self_sp) = inner_unexpected(self);
+        let (fork_unexp, fork_sp) = inner_unexpected(fork);
+        if !Rc::ptr_eq(&self_unexp, &fork_unexp) {
+            match (fork_sp, self_sp) {
+                // Unexpected set on the fork, but not on `self`, copy it over.
+                (Some((span, delimiter)), None) => {
+                    self_unexp.set(Unexpected::Some(span, delimiter));
+                }
+                // Unexpected unset. Use chain to propagate errors from fork.
+                (None, None) => {
+                    fork_unexp.set(Unexpected::Chain(self_unexp));
+
+                    // Ensure toplevel 'unexpected' tokens from the fork don't
+                    // propagate up the chain by replacing the root `unexpected`
+                    // pointer, only 'unexpected' tokens from existing group
+                    // parsers should propagate.
+                    fork.unexpected
+                        .set(Some(Rc::new(Cell::new(Unexpected::None))));
+                }
+                // Unexpected has been set on `self`. No changes needed.
+                (_, Some(_)) => {}
+            }
+        }
+
+        // See comment on `cell` in the struct definition.
+        self.cell
+            .set(unsafe { mem::transmute::<Cursor, Cursor<'static>>(fork.cursor()) });
+    }
+}
+
+/// Extensions to the `ParseStream` API to support manipulating invisible
+/// delimiters the same as if they were visible.
+pub trait AnyDelimiter {
+    /// Returns the delimiter, the span of the delimiter token, and the nested
+    /// contents for further parsing.
+    fn parse_any_delimiter(&self) -> Result<(Delimiter, DelimSpan, ParseBuffer)>;
+}
+
+impl<'a> AnyDelimiter for ParseBuffer<'a> {
+    fn parse_any_delimiter(&self) -> Result<(Delimiter, DelimSpan, ParseBuffer)> {
+        self.step(|cursor| {
+            if let Some((content, delimiter, span, rest)) = cursor.any_group() {
+                let scope = span.close();
+                let nested = crate::parse::advance_step_cursor(cursor, content);
+                let unexpected = crate::parse::get_unexpected(self);
+                let content = crate::parse::new_parse_buffer(scope, nested, unexpected);
+                Ok(((delimiter, span, content), rest))
+            } else {
+                Err(cursor.error("expected any delimiter"))
+            }
+        })
+    }
+}