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e11ec65cc8
RCU's dyntick-idle code is written to tolerate half-interrupts, that it, either an interrupt that invokes rcu_irq_enter() but never invokes the corresponding rcu_irq_exit() on the one hand, or an interrupt that never invokes rcu_irq_enter() but does invoke the "corresponding" rcu_irq_exit() on the other. These things really did happen at one time, as evidenced by this ca-2011 LKML post: http://lkml.kernel.org/r/20111014170019.GE2428@linux.vnet.ibm.com The reason why RCU tolerates half-interrupts is that usermode helpers used exceptions to invoke a system call from within the kernel such that the system call did a normal return (not a return from exception) to the calling context. This caused rcu_irq_enter() to be invoked without a matching rcu_irq_exit(). However, usermode helpers have since been rewritten to make much more housebroken use of workqueues, kernel threads, and do_execve(), and therefore should no longer produce half-interrupts. No one knows of any other source of half-interrupts, but then again, no one seems insane enough to go audit the entire kernel to verify that half-interrupts really are a relic of the past. This commit therefore adds a pair of WARN_ON_ONCE() calls that will trigger in the presence of half interrupts, which the code will continue to handle correctly. If neither of these WARN_ON_ONCE() trigger by mid-2021, then perhaps RCU can stop handling half-interrupts, which would be a considerable simplification. Reported-by: Steven Rostedt <rostedt@goodmis.org> Reported-by: Joel Fernandes <joel@joelfernandes.org> Reported-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> |
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| .. | ||
| Kconfig | ||
| Kconfig.debug | ||
| Makefile | ||
| rcu.h | ||
| rcu_segcblist.c | ||
| rcu_segcblist.h | ||
| rcuperf.c | ||
| rcutorture.c | ||
| srcutiny.c | ||
| srcutree.c | ||
| sync.c | ||
| tiny.c | ||
| tree.c | ||
| tree.h | ||
| tree_exp.h | ||
| tree_plugin.h | ||
| update.c | ||