From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Tue, 23 Mar 2010 23:27:50 +0000 (-0700)
Subject: HAMMER VFS - Fix another low memory deadlock issue
X-Git-Tag: v2.7.0~28^2~4
X-Git-Url: https://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/1205225348c6b0af2fa0b8dea95c18d2dca61763

HAMMER VFS - Fix another low memory deadlock issue

* Unlock the cursor around calls to vm_wait_nominal() to avoid deadlocking
  while holding shared node locks.

* Add vm_test_nominal() which returns TRUE if vm_wait_nominal() would
  block.

Reported-by: Francois Tigeot <ftigeot@wolfpond.org>
---

diff --git a/sys/vfs/hammer/hammer_rebalance.c b/sys/vfs/hammer/hammer_rebalance.c
index 5390aa2935..e2326179bb 100644
--- a/sys/vfs/hammer/hammer_rebalance.c
+++ b/sys/vfs/hammer/hammer_rebalance.c
@@ -119,7 +119,11 @@ retry:
 		 * Rebalancing can be hard on the memory allocator, make
 		 * sure there is enough free memory before doing it.
 		 */
-		vm_wait_nominal();
+		if (vm_test_nominal()) {
+			hammer_unlock_cursor(&cursor);
+			vm_wait_nominal();
+			hammer_lock_cursor(&cursor);
+		}
 
 		/*
 		 * We only care about internal nodes visited for the last
diff --git a/sys/vm/vm_extern.h b/sys/vm/vm_extern.h
index 49fa4b9eb9..eb5e914264 100644
--- a/sys/vm/vm_extern.h
+++ b/sys/vm/vm_extern.h
@@ -96,6 +96,7 @@ int vm_fault_wire (vm_map_t, vm_map_entry_t, boolean_t);
 void vm_fork (struct proc *, struct proc *, int);
 void vm_fault_ratecheck(void);
 void vm_waitproc (struct proc *);
+int vm_test_nominal (void);
 void vm_wait_nominal (void);
 void vm_init_limits(struct proc *);
 
diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
index 2a20a2377a..6b57cc3a4f 100644
--- a/sys/vm/vm_page.c
+++ b/sys/vm/vm_page.c
@@ -845,6 +845,17 @@ vm_wait_nominal(void)
 		vm_wait(0);
 }
 
+/*
+ * Test if vm_wait_nominal() would block.
+ */
+int
+vm_test_nominal(void)
+{
+	if (vm_page_count_min(0))
+		return(1);
+	return(0);
+}
+
 /*
  * Block until free pages are available for allocation, called in various
  * places before memory allocations.