From 034dd340b08be1f2f0477ad16131d609f9dbd53c Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 30 Aug 2026 09:22:00 -0700 Subject: Merge tag 'trace-v7.3-2' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace 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 --- rust/syn/discouraged.rs | 227 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 227 insertions(+) create mode 100644 rust/syn/discouraged.rs (limited to 'rust/syn/discouraged.rs') 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::` no longer required by accepting + /// `path::to` 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 From for PathSegment + /// # where + /// # T: Into, + /// # { + /// # fn from(ident: T) -> Self { + /// # PathSegment { + /// # ident: ident.into(), + /// # arguments: PathArguments::None, + /// # } + /// # } + /// # } + /// + /// impl Parse for PathSegment { + /// fn parse(input: ParseStream) -> Result { + /// 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::("a").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::>(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")) + } + }) + } +} -- cgit v1.3.1