.32 patches

2 files changed, 83 insertions, 0 deletions

diff --git a/queue-2.6.32/fix-time-inconsistencies-caused-by-intermediate-xtime_cache-values-being-read.patch b/queue-2.6.32/fix-time-inconsistencies-caused-by-intermediate-xtime_cache-values-being-read.patch
new file mode 100644
index 0000000..8020ff3
--- /dev/null
+++ b/queue-2.6.32/fix-time-inconsistencies-caused-by-intermediate-xtime_cache-values-being-read.patch
@@ -0,0 +1,82 @@
+From johnstul@us.ibm.com  Wed May 11 16:20:57 2011
+From: john stultz <johnstul@us.ibm.com>
+Date: Wed, 11 May 2011 16:10:28 -0700
+Subject: Fix time() inconsistencies caused by intermediate xtime_cache values being read
+To: stable@kernel.org
+Cc: Greg KH <gregkh@suse.de>, Eric Dumazet <eric.dumazet@gmail.com>, sfr@au1.ibm.com, Max Asbock <masbock@linux.vnet.ibm.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Andi Kleen <andi@firstfloor.org>
+Message-ID: <1305155428.2680.2.camel@work-vm>
+
+
+Currently with 2.6.32-longterm, its possible for time() to occasionally
+return values one second earlier then the previous time() call.
+
+This happens because update_xtime_cache() does:
+	xtime_cache = xtime;
+	timespec_add_ns(&xtime_cache, nsec);
+
+Its possible that xtime is 1sec,999msecs, and nsecs is 1ms, resulting in
+a xtime_cache that is 2sec,0ms.
+
+get_seconds() (which is used by sys_time()) does not take the
+xtime_lock, which is ok as the xtime.tv_sec value is a long and can be
+atomically read safely.
+
+The problem occurs the next call to update_xtime_cache() if xtime has
+not increased:
+	/* This sets xtime_cache back to 1sec, 999msec */
+	xtime_cache = xtime; 
+	/* get_seconds, calls here, and sees a 1second inconsistency */
+	timespec_add_ns(&xtime_cache, nsec);
+
+
+In order to resolve this, we could add locking to get_seconds(), but it
+needs to be lock free, as it is called from the machine check handler,
+opening a possible deadlock.
+
+So instead, this patch introduces an intermediate value for the
+calculations, so that we only assign xtime_cache once with the correct
+time, using ACCESS_ONCE to make sure the compiler doesn't optimize out
+any intermediate values.
+
+The xtime_cache manipulations were removed with 2.6.35, so that kernel
+and later do not need this change.
+
+In 2.6.33 and 2.6.34 the logarithmic accumulation should make it so
+xtime is updated each tick, so it is unlikely that two updates to
+xtime_cache could occur while the difference between xtime and
+xtime_cache crosses the second boundary. However, the paranoid might
+want to pull this into 2.6.33/34-longterm just to be sure.
+
+Thanks to Stephen for helping finally narrow down the root cause and
+many hours of help with testing and validation. Also thanks to Max,
+Andi, Eric and Paul for review of earlier attempts and helping clarify
+what is possible with regard to out of order execution.
+
+Acked-by: Eric Dumazet <eric.dumazet@gmail.com>
+Signed-off-by: John Stultz <johnstul@us.ibm.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
+
+---
+ kernel/time/timekeeping.c |   11 +++++++++--
+ 1 file changed, 9 insertions(+), 2 deletions(-)
+
+--- a/kernel/time/timekeeping.c
++++ b/kernel/time/timekeeping.c
+@@ -168,8 +168,15 @@ int __read_mostly timekeeping_suspended;
+ static struct timespec xtime_cache __attribute__ ((aligned (16)));
+ void update_xtime_cache(u64 nsec)
+ {
+-	xtime_cache = xtime;
+-	timespec_add_ns(&xtime_cache, nsec);
++	/*
++	 * Use temporary variable so get_seconds() cannot catch
++	 * an intermediate xtime_cache.tv_sec value.
++	 * The ACCESS_ONCE() keeps the compiler from optimizing
++	 * out the intermediate value.
++	 */
++	struct timespec ts = xtime;
++	timespec_add_ns(&ts, nsec);
++	ACCESS_ONCE(xtime_cache) = ts;
+ }
+ 
+ /* must hold xtime_lock */
diff --git a/queue-2.6.32/series b/queue-2.6.32/series
index 9db9496..0c61008 100644
--- a/queue-2.6.32/series
+++ b/queue-2.6.32/series
@@ -2,3 +2,4 @@ cifs-check-for-bytes_remaining-going-to-zero-in-cifs_sesssetup.patch
 validate-size-of-efi-guid-partition-entries.patch
 dccp-handle-invalid-feature-options-length.patch
 cifs-fix-memory-over-bound-bug-in-cifs_parse_mount_options.patch
+fix-time-inconsistencies-caused-by-intermediate-xtime_cache-values-being-read.patch