From fa609f4d93f798de2153e04476f9b825aa469491 Mon Sep 17 00:00:00 2001 From: kib Date: Tue, 24 Apr 2012 17:51:36 +0000 Subject: Take the spinlock around clearing of the fp->_flags in fclose(3), which indicates the avaliability of FILE, to prevent possible reordering of the writes as seen by other CPUs. Reported by: Fengwei yin Reviewed by: jhb MFC after: 1 week --- lib/libc/stdio/fclose.c | 14 ++++++++++++++ lib/libc/stdio/findfp.c | 16 +++++++--------- 2 files changed, 21 insertions(+), 9 deletions(-) (limited to 'lib/libc/stdio') diff --git a/lib/libc/stdio/fclose.c b/lib/libc/stdio/fclose.c index f0629e8..3957b6a 100644 --- a/lib/libc/stdio/fclose.c +++ b/lib/libc/stdio/fclose.c @@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$"); #include #include #include "un-namespace.h" +#include #include "libc_private.h" #include "local.h" @@ -65,7 +66,20 @@ fclose(FILE *fp) FREELB(fp); fp->_file = -1; fp->_r = fp->_w = 0; /* Mess up if reaccessed. */ + + /* + * Lock the spinlock used to protect __sglue list walk in + * __sfp(). The __sfp() uses fp->_flags == 0 test as an + * indication of the unused FILE. + * + * Taking the lock prevents possible compiler or processor + * reordering of the writes performed before the final _flags + * cleanup, making sure that we are done with the FILE before + * it is considered available. + */ + STDIO_THREAD_LOCK(); fp->_flags = 0; /* Release this FILE for reuse. */ + STDIO_THREAD_UNLOCK(); FUNLOCKFILE(fp); return (r); } diff --git a/lib/libc/stdio/findfp.c b/lib/libc/stdio/findfp.c index 89c0536..6d0b673 100644 --- a/lib/libc/stdio/findfp.c +++ b/lib/libc/stdio/findfp.c @@ -82,9 +82,7 @@ static struct glue *lastglue = &uglue; static struct glue * moreglue(int); -static spinlock_t thread_lock = _SPINLOCK_INITIALIZER; -#define THREAD_LOCK() if (__isthreaded) _SPINLOCK(&thread_lock) -#define THREAD_UNLOCK() if (__isthreaded) _SPINUNLOCK(&thread_lock) +spinlock_t __stdio_thread_lock = _SPINLOCK_INITIALIZER; #if NOT_YET #define SET_GLUE_PTR(ptr, val) atomic_set_rel_ptr(&(ptr), (uintptr_t)(val)) @@ -127,22 +125,22 @@ __sfp() /* * The list must be locked because a FILE may be updated. */ - THREAD_LOCK(); + STDIO_THREAD_LOCK(); for (g = &__sglue; g != NULL; g = g->next) { for (fp = g->iobs, n = g->niobs; --n >= 0; fp++) if (fp->_flags == 0) goto found; } - THREAD_UNLOCK(); /* don't hold lock while malloc()ing. */ + STDIO_THREAD_UNLOCK(); /* don't hold lock while malloc()ing. */ if ((g = moreglue(NDYNAMIC)) == NULL) return (NULL); - THREAD_LOCK(); /* reacquire the lock */ + STDIO_THREAD_LOCK(); /* reacquire the lock */ SET_GLUE_PTR(lastglue->next, g); /* atomically append glue to list */ lastglue = g; /* not atomic; only accessed when locked */ fp = g->iobs; found: fp->_flags = 1; /* reserve this slot; caller sets real flags */ - THREAD_UNLOCK(); + STDIO_THREAD_UNLOCK(); fp->_p = NULL; /* no current pointer */ fp->_w = 0; /* nothing to read or write */ fp->_r = 0; @@ -183,10 +181,10 @@ f_prealloc(void) for (g = &__sglue; (n -= g->niobs) > 0 && g->next; g = g->next) /* void */; if ((n > 0) && ((g = moreglue(n)) != NULL)) { - THREAD_LOCK(); + STDIO_THREAD_LOCK(); SET_GLUE_PTR(lastglue->next, g); lastglue = g; - THREAD_UNLOCK(); + STDIO_THREAD_UNLOCK(); } } -- cgit v1.1