Revert fwalk/sfp locking to fix concurrent reads
The locking can fail in a couple of ways:
- A concurrent fread from an unbuffered or line-buffered file flushes
the output of other line-buffered files, and if _fwalk locks every
file, then the fread blocks until other file reads have completed.
- __sfp can initialize a file lock while _fwalk is locking/unlocking it.
For now, revert to the behavior Bionic had in previous releases. This
commit reverts the file locking parts of commit
468efc80da2504f4ae7de8b5e137426d44dda9d7.
Bug: http://b/131251441
Bug: http://b/130189834
Test: bionic unit tests
Change-Id: I9e20b9cd8ccd14e7962f7308e174f08af72b56c6
diff --git a/libc/stdio/stdio.cpp b/libc/stdio/stdio.cpp
index 4cec757..91c7689 100644
--- a/libc/stdio/stdio.cpp
+++ b/libc/stdio/stdio.cpp
@@ -106,7 +106,7 @@
FILE* stdout = &__sF[1];
FILE* stderr = &__sF[2];
-static pthread_mutex_t __stdio_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
+static pthread_mutex_t __stdio_mutex = PTHREAD_MUTEX_INITIALIZER;
static uint64_t __get_file_tag(FILE* fp) {
// Don't use a tag for the standard streams.
@@ -211,21 +211,23 @@
}
int _fwalk(int (*callback)(FILE*)) {
- pthread_mutex_lock(&__stdio_mutex);
int result = 0;
for (glue* g = &__sglue; g != nullptr; g = g->next) {
FILE* fp = g->iobs;
for (int n = g->niobs; --n >= 0; ++fp) {
- ScopedFileLock sfl(fp);
if (fp->_flags != 0 && (fp->_flags & __SIGN) == 0) {
result |= (*callback)(fp);
}
}
}
- pthread_mutex_unlock(&__stdio_mutex);
return result;
}
+extern "C" __LIBC_HIDDEN__ void __libc_stdio_cleanup(void) {
+ // Equivalent to fflush(nullptr), but without all the locking since we're shutting down anyway.
+ _fwalk(__sflush);
+}
+
static FILE* __fopen(int fd, int flags) {
#if !defined(__LP64__)
if (fd > SHRT_MAX) {
@@ -520,6 +522,11 @@
return 0;
}
+int __sflush_locked(FILE* fp) {
+ ScopedFileLock sfl(fp);
+ return __sflush(fp);
+}
+
int __sread(void* cookie, char* buf, int n) {
FILE* fp = reinterpret_cast<FILE*>(cookie);
return TEMP_FAILURE_RETRY(read(fp->_file, buf, n));
@@ -1061,7 +1068,7 @@
}
static int fflush_all() {
- return _fwalk(__sflush);
+ return _fwalk(__sflush_locked);
}
int fflush(FILE* fp) {