Attachment 98081 Details for Bug 136918 – file.diff

[patch] file.diff

file.diff (text/plain), 3.68 KB, created by Ben Kaduk on 2009-07-20 06:00:12 UTC

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Creator: Ben Kaduk

Created: 2009-07-20 06:00:12 UTC

Size: 3.68 KB

patch

obsolete

>--- locking.9.orig      2009-07-18 15:15:25.000000000 -0400
>+++ locking.9   2009-07-20 00:34:46.000000000 -0400
>@@ -77,8 +77,8 @@
> Some of these primitives may be used at the low (interrupt) level and
> some may not.
> .Pp
>-There are strict ordering requirements and for some of the types this
>-is checked using the
>+There are strict ordering requirements for the different lock types,
>+and for some of the types this ordering is checked using the
> .Xr witness 4
> code.
> .Pp
>@@ -98,9 +98,10 @@
> A non-spin mutex can be considered to be equivalent
> to getting a write lock on an
> .Em rw_lock
>-(see below), and in fact non-spin mutexes and rw_locks may soon become the same thing.
>-As in spin mutexes, you either get it or you don't.
>-You may only call the
>+(see below), and in fact non-spin mutexes and rw_locks
>+may soon become the same thing.
>+As for spin mutexes, you either get it or you don't.
>+While holding a mutex, you may only call the
> .Xr sleep 9
> call via
> .Fn msleep
>@@ -111,20 +112,22 @@
> as part of waking up.
> This is often however a
> .Em BAD
>-idea because it generally relies on you having
>+idea because it generally relies on you the programmer having
> such a good knowledge of all the call graph above you
>-and what assumptions it is making that there are a lot
>+and what assumptions the calling code has made that there are a lot
> of ways to make hard-to-find mistakes.
>-For example you MUST re-test all the assumptions you made before,
>-all the way up the call graph to where you got the lock.
>-You can not just assume that mtx_sleep can be inserted anywhere.
>-If any caller above you has any mutex or
>-rwlock, your sleep, will cause a panic.
>+For example you MUST re-test all the assumptions that were made before
>+acquiring the lock, in all the levels of the call graph.
>+You can not just assume that a
>+.Fn mtx_sleep
>+can be inserted anywhere.
>+If any caller above you holds any mutex or
>+rwlock, your sleep will cause a panic.
> If the sleep only happens rarely it may be years before the
> bad code path is found.
> .Ss Pool Mutexes
>-A variant of regular mutexes where the allocation of the mutex is handled
>-more by the system.
>+A variant of regular mutexes where the allocation of the mutex is
>+largely handled by the system.
> .Ss Rw_locks
> Reader/writer locks allow shared access to protected data by multiple threads,
> or exclusive access by a single thread.
>@@ -173,7 +176,7 @@
> locking.
> .Em rm_lock
> locks implement full priority propagation by tracking shared owners
>-using a lock user supplied
>+using a caller-supplied
> .Em tracker
> data structure.
> .Ss Sx_locks
>@@ -205,11 +208,12 @@
> Turnstiles are used to hold a queue of threads blocked on
> non-sleepable locks.
> Sleepable locks use condition variables to implement their queues.
>-Turnstiles differ from a sleep queue in that turnstile queue's
>-are assigned to a lock held by an owning thread.
>-Thus, when one thread is enqueued onto a turnstile, it can lend its
>-priority to the owning thread.
>-If this sounds confusing, we need to describe it better.
>+Turnstiles differ from sleep queues in that turnstile queues
>+are assigned to a lock held by an owning thread, whereas
>+there is a global hash table of active sleep queues
>+Thus, when a thread running at a high priority is enqueued onto
>+a turnstile, its priority can propagate to the thread that holds
>+the lock, helping to avoid a deadlock situation.
> .Ss Semaphores
> .Ss Condition variables
> Condition variables are used in conjunction with mutexes to wait for
>@@ -329,7 +333,7 @@
> Lock order is important.
> .Pp
> .Em *3
>-There are calls atomically release this primitive when going to sleep
>+There are calls that atomically release this primitive when going to sleep
> and reacquire it on wakeup (e.g.
> .Fn mtx_sleep ,
> .Fn rw_sleep

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