1. Does the update code have proper mutual exclusion?
- RCU does allow -readers- to run (almost) naked, but -writers- must
+ RCU does allow *readers* to run (almost) naked, but *writers* must
still use some sort of mutual exclusion, such as:
a. locking,
critical section is every bit as bad as letting them leak out
from under a lock. Unless, of course, you have arranged some
other means of protection, such as a lock or a reference count
- -before- letting them out of the RCU read-side critical section.
+ *before* letting them out of the RCU read-side critical section.
3. Does the update code tolerate concurrent accesses?
c. Make updates appear atomic to readers. For example,
pointer updates to properly aligned fields will
appear atomic, as will individual atomic primitives.
- Sequences of operations performed under a lock will -not-
+ Sequences of operations performed under a lock will *not*
appear to be atomic to RCU readers, nor will sequences
of multiple atomic primitives.
for example) may be omitted.
10. Conversely, if you are in an RCU read-side critical section,
- and you don't hold the appropriate update-side lock, you -must-
+ and you don't hold the appropriate update-side lock, you *must*
use the "_rcu()" variants of the list macros. Failing to do so
will break Alpha, cause aggressive compilers to generate bad code,
and confuse people trying to read your code.
callback pending, then that RCU callback will execute on some
surviving CPU. (If this was not the case, a self-spawning RCU
callback would prevent the victim CPU from ever going offline.)
- Furthermore, CPUs designated by rcu_nocbs= might well -always-
+ Furthermore, CPUs designated by rcu_nocbs= might well *always*
have their RCU callbacks executed on some other CPUs, in fact,
for some real-time workloads, this is the whole point of using
the rcu_nocbs= kernel boot parameter.
-13. Unlike other forms of RCU, it -is- permissible to block in an
+13. Unlike other forms of RCU, it *is* permissible to block in an
SRCU read-side critical section (demarked by srcu_read_lock()
and srcu_read_unlock()), hence the "SRCU": "sleepable RCU".
Please note that if you don't need to sleep in read-side critical
14. The whole point of call_rcu(), synchronize_rcu(), and friends
is to wait until all pre-existing readers have finished before
carrying out some otherwise-destructive operation. It is
- therefore critically important to -first- remove any path
+ therefore critically important to *first* remove any path
that readers can follow that could be affected by the
- destructive operation, and -only- -then- invoke call_rcu(),
+ destructive operation, and *only then* invoke call_rcu(),
synchronize_rcu(), or friends.
Because these primitives only wait for pre-existing readers, it
is the caller's responsibility to guarantee that any subsequent
readers will execute safely.
-15. The various RCU read-side primitives do -not- necessarily contain
+15. The various RCU read-side primitives do *not* necessarily contain
memory barriers. You should therefore plan for the CPU
and the compiler to freely reorder code into and out of RCU
read-side critical sections. It is the responsibility of the
pass in a function defined within a loadable module, then it in
necessary to wait for all pending callbacks to be invoked after
the last invocation and before unloading that module. Note that
- it is absolutely -not- sufficient to wait for a grace period!
- The current (say) synchronize_rcu() implementation is -not-
+ it is absolutely *not* sufficient to wait for a grace period!
+ The current (say) synchronize_rcu() implementation is *not*
guaranteed to wait for callbacks registered on other CPUs.
Or even on the current CPU if that CPU recently went offline
and came back online.
- call_rcu() -> rcu_barrier()
- call_srcu() -> srcu_barrier()
- However, these barrier functions are absolutely -not- guaranteed
+ However, these barrier functions are absolutely *not* guaranteed
to wait for a grace period. In fact, if there are no call_rcu()
callbacks waiting anywhere in the system, rcu_barrier() is within
its rights to return immediately.
projects / linux-2.6-microblaze.git / blobdiff