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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-06-28 22:45:23 +0300 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-08-31 02:02:36 +0300 |
commit | e11ec65cc8d63c41fc468363b65826a5ae4b8c66 (patch) | |
tree | cf8fc0b086e673a109889d308e906722d5d22c77 /include/linux/rcutiny.h | |
parent | fcc878e4dfb70128a73857c609d70570629b0d9e (diff) | |
download | linux-e11ec65cc8d63c41fc468363b65826a5ae4b8c66.tar.xz |
rcu: Add warning to detect half-interrupts
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>
Diffstat (limited to 'include/linux/rcutiny.h')
0 files changed, 0 insertions, 0 deletions