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Diffstat (limited to 'Documentation/RCU/Design/Requirements/Requirements.htmlx')
| -rw-r--r-- | Documentation/RCU/Design/Requirements/Requirements.htmlx | 25 |
1 files changed, 24 insertions, 1 deletions
diff --git a/Documentation/RCU/Design/Requirements/Requirements.htmlx b/Documentation/RCU/Design/Requirements/Requirements.htmlx index a544db4646c6..23524d75a3c3 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.htmlx +++ b/Documentation/RCU/Design/Requirements/Requirements.htmlx @@ -1777,12 +1777,35 @@ guard against mishaps and misuse: supplied the needed <a href="https://lkml.kernel.org/g/20100319013024.GA28456@Krystal">patch</a>. <li> An infinite loop in an RCU read-side critical section will - eventually trigger an RCU CPU stall warning splat. + eventually trigger an RCU CPU stall warning splat, with + the duration of “eventually” being controlled by the + <tt>RCU_CPU_STALL_TIMEOUT</tt> <tt>Kconfig</tt> option, or, + alternatively, by the + <tt>rcupdate.rcu_cpu_stall_timeout</tt> boot/sysfs + parameter. However, RCU is not obligated to produce this splat unless there is a grace period waiting on that particular RCU read-side critical section. + <p> + Some extreme workloads might intentionally delay + RCU grace periods, and systems running those workloads can + be booted with <tt>rcupdate.rcu_cpu_stall_suppress</tt> + to suppress the splats. + This kernel parameter may also be set via <tt>sysfs</tt>. + Furthermore, RCU CPU stall warnings are counter-productive + during sysrq dumps and during panics. + RCU therefore supplies the <tt>rcu_sysrq_start()</tt> and + <tt>rcu_sysrq_end()</tt> API members to be called before + and after long sysrq dumps. + RCU also supplies the <tt>rcu_panic()</tt> notifier that is + automatically invoked at the beginning of a panic to suppress + further RCU CPU stall warnings. + + <p> This requirement made itself known in the early 1990s, pretty much the first time that it was necessary to debug a CPU stall. + That said, the initial implementation in DYNIX/ptx was quite + generic in comparison with that of Linux. <li> Although it would be very good to detect pointers leaking out of RCU read-side critical sections, there is currently no good way of doing this. |