Patch "clocksource: Reduce the default clocksource_watchdog() retries to 2" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    clocksource: Reduce the default clocksource_watchdog() retries to 2

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     clocksource-reduce-the-default-clocksource_watchdog-.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 9f679a1f2aa7e738e3ab7b445627942659d962a8
Author: Waiman Long <longman@xxxxxxxxxx>
Date:   Thu Nov 18 14:14:37 2021 -0500

    clocksource: Reduce the default clocksource_watchdog() retries to 2
    
    [ Upstream commit 1a5620671a1b6fd9cc08761677d050f1702f910c ]
    
    With the previous patch, there is an extra watchdog read in each retry.
    Now the total number of clocksource reads is increased to 4 per iteration.
    In order to avoid increasing the clock skew check overhead, the default
    maximum number of retries is reduced from 3 to 2 to maintain the same 12
    clocksource reads in the worst case.
    
    Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
    Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
    Stable-dep-of: f2655ac2c06a ("clocksource: Fix brown-bag boolean thinko in cs_watchdog_read()")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index d49e11962333c..2db3d5b6fc038 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -603,8 +603,8 @@
 	clocksource.max_cswd_read_retries= [KNL]
 			Number of clocksource_watchdog() retries due to
 			external delays before the clock will be marked
-			unstable.  Defaults to three retries, that is,
-			four attempts to read the clock under test.
+			unstable.  Defaults to two retries, that is,
+			three attempts to read the clock under test.
 
 	clocksource.verify_n_cpus= [KNL]
 			Limit the number of CPUs checked for clocksources
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 7d6d87a22ad55..38bb654d2a7e1 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -201,7 +201,7 @@ void clocksource_mark_unstable(struct clocksource *cs)
 	spin_unlock_irqrestore(&watchdog_lock, flags);
 }
 
-ulong max_cswd_read_retries = 3;
+ulong max_cswd_read_retries = 2;
 module_param(max_cswd_read_retries, ulong, 0644);
 EXPORT_SYMBOL_GPL(max_cswd_read_retries);
 static int verify_n_cpus = 8;