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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-08-04 21:54:04 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2015-10-06 21:22:38 +0300
commitda873def8da5883a6c04d11f73dcd836c216cf4f (patch)
tree31acd41769b785280e4af9a69964f5974841fe6b /Documentation/RCU
parent27566139b6e2f6cfe273e8bb0e538d7616c2ea00 (diff)
downloadlinux-da873def8da5883a6c04d11f73dcd836c216cf4f.tar.xz
documentation: Call out slow consoles as cause of stall warnings
The Linux kernel outputs copious text during boot, and a slow serial console can result in stall warnings, particularly when messages are printed with interrupts disabled. This commit adds this to the list of causes of RCU CPU stall warning messages. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Diffstat (limited to 'Documentation/RCU')
-rw-r--r--Documentation/RCU/stallwarn.txt7
1 files changed, 7 insertions, 0 deletions
diff --git a/Documentation/RCU/stallwarn.txt b/Documentation/RCU/stallwarn.txt
index efb9454875ab..0f7fb4298e7e 100644
--- a/Documentation/RCU/stallwarn.txt
+++ b/Documentation/RCU/stallwarn.txt
@@ -205,6 +205,13 @@ o For !CONFIG_PREEMPT kernels, a CPU looping anywhere in the
behavior, you might need to replace some of the cond_resched()
calls with calls to cond_resched_rcu_qs().
+o Booting Linux using a console connection that is too slow to
+ keep up with the boot-time console-message rate. For example,
+ a 115Kbaud serial console can be -way- too slow to keep up
+ with boot-time message rates, and will frequently result in
+ RCU CPU stall warning messages. Especially if you have added
+ debug printk()s.
+
o Anything that prevents RCU's grace-period kthreads from running.
This can result in the "All QSes seen" console-log message.
This message will include information on when the kthread last