svn commit: r203759 - head/share/man/man9
Edward Tomasz Napierala
trasz at FreeBSD.org
Wed Feb 10 17:02:06 UTC 2010
Author: trasz
Date: Wed Feb 10 17:02:06 2010
New Revision: 203759
URL: http://svn.freebsd.org/changeset/base/203759
Log:
Improve description for Giant and mention blocking inside interrupt threads.
Modified:
head/share/man/man9/locking.9
Modified: head/share/man/man9/locking.9
==============================================================================
--- head/share/man/man9/locking.9 Wed Feb 10 16:30:04 2010 (r203758)
+++ head/share/man/man9/locking.9 Wed Feb 10 17:02:06 2010 (r203759)
@@ -24,7 +24,7 @@
.\"
.\" $FreeBSD$
.\"
-.Dd January 29, 2010
+.Dd February 10, 2010
.Dt LOCKING 9
.Os
.Sh NAME
@@ -191,13 +191,16 @@ Giant is an instance of a mutex, with so
.It
It is recursive.
.It
-Drivers can request that Giant be locked around them, but this is
-going away.
-.It
-You can sleep while it has recursed, but other recursive locks cannot.
+Drivers and filesystems can request that Giant be locked around them
+by not marking themselves MPSAFE. Note that infrastructure to do this
+is slowly going away as non-MPSAFE drivers either became properly locked
+or disappear.
.It
Giant must be locked first before other locks.
.It
+It is OK to hold Giant while performing unbounded sleep; in such case,
+Giant will be dropped before sleeping and picked up after wakeup.
+.It
There are places in the kernel that drop Giant and pick it back up
again.
Sleep locks will do this before sleeping.
@@ -315,6 +318,9 @@ If any caller above you has any mutex or
rwlock, your sleep, will cause a panic.
If the sleep only happens rarely it may be years before the
bad code path is found.
+.Pp
+It is an error to do any operation that could result in unbounded sleep when
+running inside an interrupt thread.
.Ss Interaction table
The following table shows what you can and can not do if you hold
one of the synchronization primitives discussed here:
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