Rollup merge of rust-lang#144210 - Gelbpunkt:thread-stack-size-musl, r=jhpratt

std: thread: Return error if setting thread stack size fails

Currently, when setting the thread stack size fails, it would be rounded up to the nearest multiple of the page size and the code asserts that the next call to `pthread_attr_setstacksize` succeeds.

This may be true for glibc, but it isn't true for musl, which not only enforces a minimum stack size, but also a maximum stack size of `usize::MAX / 4 - PTHREAD_STACK_MIN` [1], triggering the assert rather than erroring gracefully.

There isn't any way to handle this properly other than bailing out and letting the user know it didn't succeed.

[1]: https://git.musl-libc.org/cgit/musl/tree/src/thread/pthread_attr_setstacksize.c#n5

Author: Zalathar

library/std/src/sys/pal/unix/thread.rs

@@ -77,7 +77,15 @@ impl Thread {
                     let page_size = os::page_size();
                     let stack_size =
                         (stack_size + page_size - 1) & (-(page_size as isize - 1) as usize - 1);
-                    assert_eq!(libc::pthread_attr_setstacksize(attr.as_mut_ptr(), stack_size), 0);
+
+                    // Some libc implementations, e.g. musl, place an upper bound
+                    // on the stack size, in which case we can only gracefully return
+                    // an error here.
+                    if libc::pthread_attr_setstacksize(attr.as_mut_ptr(), stack_size) != 0 {
+                        assert_eq!(libc::pthread_attr_destroy(attr.as_mut_ptr()), 0);
+                        drop(Box::from_raw(data));
+                        return Err(io::Error::other("invalid stack size"));
+                    }
                 }
             };
         }