From: Rich Felker <dalias@aerifal.cx>
Date: Mon, 10 Dec 2012 23:31:39 +0000 (-0500)
Subject: document self-synchronized destruction issue for stdio locking
X-Git-Tag: v0.9.9~63
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=f1c1a5ea8295a3f8e9ea2db8961c5a68e1a3f9ed;p=oweals%2Fmusl.git

document self-synchronized destruction issue for stdio locking
---

diff --git a/src/stdio/__lockfile.c b/src/stdio/__lockfile.c
index 3bf3c26b..9d967d6e 100644
--- a/src/stdio/__lockfile.c
+++ b/src/stdio/__lockfile.c
@@ -14,5 +14,15 @@ int __lockfile(FILE *f)
 void __unlockfile(FILE *f)
 {
 	a_store(&f->lock, 0);
+
+	/* The following read is technically invalid under situations
+	 * of self-synchronized destruction. Another thread may have
+	 * called fclose as soon as the above store has completed.
+	 * Nonetheless, since FILE objects always live in memory
+	 * obtained by malloc from the heap, it's safe to assume
+	 * the dereferences below will not fault. In the worst case,
+	 * a spurious syscall will be made. If the implementation of
+	 * malloc changes, this assumption needs revisiting. */
+
 	if (f->waiters) __wake(&f->lock, 1, 1);
 }