Attachment 178720 Details for Bug 215826 – Fix nested write locks for the compat rtld locking.

[patch] Fix nested write locks for the compat rtld locking.

1.patch (text/plain), 3.19 KB, created by Konstantin Belousov on 2017-01-10 15:21:38 UTC

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Creator: Konstantin Belousov

Created: 2017-01-10 15:21:38 UTC

Size: 3.19 KB

patch

obsolete

>diff --git a/libexec/rtld-elf/rtld_lock.c b/libexec/rtld-elf/rtld_lock.c
>index f31546c4ac9..5c85c8cbd28 100644
>--- a/libexec/rtld-elf/rtld_lock.c
>+++ b/libexec/rtld-elf/rtld_lock.c
>@@ -38,8 +38,8 @@
>  * In this algorithm the lock is a single word.  Its low-order bit is
>  * set when a writer holds the lock.  The remaining high-order bits
>  * contain a count of readers desiring the lock.  The algorithm requires
>- * atomic "compare_and_store" and "add" operations, which we implement
>- * using assembly language sequences in "rtld_start.S".
>+ * atomic "compare_and_store" and "add" operations, which we take
>+ * from machine/atomic.h.
>  */
> 
> #include <sys/param.h>
>@@ -64,10 +64,10 @@ typedef struct Struct_Lock {
> } Lock;
> 
> static sigset_t fullsigmask, oldsigmask;
>-static int thread_flag;
>+static int thread_flag, wnested;
> 
> static void *
>-def_lock_create()
>+def_lock_create(void)
> {
>     void *base;
>     char *p;
>@@ -117,29 +117,38 @@ def_rlock_acquire(void *lock)
> static void
> def_wlock_acquire(void *lock)
> {
>-    Lock *l = (Lock *)lock;
>-    sigset_t tmp_oldsigmask;
>-
>-    for ( ; ; ) {
>-	sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
>-	if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
>-	    break;
>-	sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
>-    }
>-    oldsigmask = tmp_oldsigmask;
>+	Lock *l;
>+	sigset_t tmp_oldsigmask;
>+	int w;
>+
>+	l = (Lock *)lock;
>+	for (;;) {
>+		w = atomic_fetchadd_int(&wnested, 1);
>+		if (w == 0)
>+			sigprocmask(SIG_BLOCK, &fullsigmask, &tmp_oldsigmask);
>+		if (atomic_cmpset_acq_int(&l->lock, 0, WAFLAG))
>+			break;
>+		if (atomic_fetchadd_int(&wnested, -1) == 1)
>+			sigprocmask(SIG_SETMASK, &tmp_oldsigmask, NULL);
>+	}
>+	if (w == 0)
>+		oldsigmask = tmp_oldsigmask;
> }
> 
> static void
> def_lock_release(void *lock)
> {
>-    Lock *l = (Lock *)lock;
>-
>-    if ((l->lock & WAFLAG) == 0)
>-    	atomic_add_rel_int(&l->lock, -RC_INCR);
>-    else {
>-    	atomic_add_rel_int(&l->lock, -WAFLAG);
>-    	sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
>-    }
>+	Lock *l;
>+
>+	l = (Lock *)lock;
>+	if ((l->lock & WAFLAG) == 0)
>+		atomic_add_rel_int(&l->lock, -RC_INCR);
>+	else {
>+		assert(wnested > 0);
>+		atomic_add_rel_int(&l->lock, -WAFLAG);
>+		if (atomic_fetchadd_int(&wnested, -1) == 1)
>+			sigprocmask(SIG_SETMASK, &oldsigmask, NULL);
>+	}
> }
> 
> static int
>@@ -269,7 +278,7 @@ lock_restart_for_upgrade(RtldLockState *lockstate)
> }
> 
> void
>-lockdflt_init()
>+lockdflt_init(void)
> {
>     int i;
> 
>@@ -373,12 +382,12 @@ _rtld_atfork_pre(int *locks)
> 		return;
> 
> 	/*
>-	 * Warning: this does not work with the rtld compat locks
>-	 * above, since the thread signal mask is corrupted (set to
>-	 * all signals blocked) if two locks are taken in write mode.
>-	 * The caller of the _rtld_atfork_pre() must provide the
>-	 * working implementation of the locks, and libthr locks are
>-	 * fine.
>+	 * Warning: this did not worked well with the rtld compat
>+	 * locks above, when the thread signal mask was corrupted (set
>+	 * to all signals blocked) if two locks were taken
>+	 * simultaneously in the write mode.  The caller of the
>+	 * _rtld_atfork_pre() must provide the working implementation
>+	 * of the locks anyway, and libthr locks are fine.
> 	 */
> 	wlock_acquire(rtld_phdr_lock, &ls[0]);
> 	wlock_acquire(rtld_bind_lock, &ls[1]);

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Attachments on bug 215826: 178664 | 178670 | 178720