Author: alc
Date: Tue Nov 1 17:11:10 2016
New Revision: 308174
URL: https://svnweb.freebsd.org/changeset/base/308174
Log:
Move and revise a comment about the relation between the object's paging-
in-progress count and the vnode. Prior to r188331, we always acquired
the vnode lock before incrementing the object's paging-in-progress count.
Now, we increment it before attempting to acquire the vnode lock with
LK_NOWAIT, but we never sleep acquiring the vnode lock while we have the
count incremented.
Reviewed by: kib
MFC after: 3 days
Modified:
head/sys/vm/vm_fault.c
Modified: head/sys/vm/vm_fault.c
==============================================================================
--- head/sys/vm/vm_fault.c Tue Nov 1 16:03:31 2016 (r308173)
+++ head/sys/vm/vm_fault.c Tue Nov 1 17:11:10 2016 (r308174)
@@ -420,8 +420,7 @@ fast_failed:
* they will stay around as well.
*
* Bump the paging-in-progress count to prevent size changes (e.g.
- * truncation operations) during I/O. This must be done after
- * obtaining the vnode lock in order to avoid possible deadlocks.
+ * truncation operations) during I/O.
*/
vm_object_reference_locked(fs.first_object);
vm_object_pip_add(fs.first_object, 1);
@@ -647,7 +646,13 @@ readrest:
if (locked != LK_EXCLUSIVE)
locked = LK_SHARED;
- /* Do not sleep for vnode lock while fs.m is
busy */
+
+ /*
+ * We must not sleep acquiring the vnode lock
+ * while we have the page exclusive busied or
+ * the object's paging-in-progress count
+ * incremented. Otherwise, we could deadlock.
+ */
error = vget(vp, locked | LK_CANRECURSE |
LK_NOWAIT, curthread);
if (error != 0) {
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