diff options
Diffstat (limited to 'module/zfs/zthr.c')
| -rw-r--r-- | module/zfs/zthr.c | 54 |
1 files changed, 36 insertions, 18 deletions
diff --git a/module/zfs/zthr.c b/module/zfs/zthr.c index 64372f338..dd8505caa 100644 --- a/module/zfs/zthr.c +++ b/module/zfs/zthr.c @@ -92,7 +92,16 @@ * user should take this into account when writing a checkfunc. * [see ZTHR state transitions] * - * == ZTHR cancellation + * == ZTHR wakeup + * + * ZTHR wakeup should be used when new work is added for the zthr. The + * sleeping zthr will wakeup, see that it has more work to complete + * and proceed. This can be invoked from open or syncing context. + * + * To wakeup a zthr: + * zthr_wakeup(zthr_t *t) + * + * == ZTHR cancellation and resumption * * ZTHR threads must be cancelled when their SPA is being exported * or when they need to be paused so they don't interfere with other @@ -104,6 +113,9 @@ * To resume it: * zthr_resume(zthr_pointer); * + * ZTHR cancel and resume should be invoked in open context during the + * lifecycle of the pool as it is imported, exported or destroyed. + * * A zthr will implicitly check if it has received a cancellation * signal every time func returns and every time it wakes up [see * ZTHR state transitions below]. @@ -161,15 +173,19 @@ * * == Implementation of ZTHR requests * - * ZTHR wakeup, cancel, and resume are requests on a zthr to - * change its internal state. Requests on a zthr are serialized - * using the zthr_request_lock, while changes in its internal - * state are protected by the zthr_state_lock. A request will - * first acquire the zthr_request_lock and then immediately - * acquire the zthr_state_lock. We do this so that incoming - * requests are serialized using the request lock, while still - * allowing us to use the state lock for thread communication - * via zthr_cv. + * ZTHR cancel and resume are requests on a zthr to change its + * internal state. These requests are serialized using the + * zthr_request_lock, while changes in its internal state are + * protected by the zthr_state_lock. A request will first acquire + * the zthr_request_lock and then immediately acquire the + * zthr_state_lock. We do this so that incoming requests are + * serialized using the request lock, while still allowing us + * to use the state lock for thread communication via zthr_cv. + * + * ZTHR wakeup broadcasts to zthr_cv, causing sleeping threads + * to wakeup. It acquires the zthr_state_lock but not the + * zthr_request_lock, so that a wakeup on a zthr in the middle + * of being cancelled will not block. */ #include <sys/zfs_context.h> @@ -287,17 +303,16 @@ zthr_destroy(zthr_t *t) } /* - * Wake up the zthr if it is sleeping. If the thread has been - * cancelled that does nothing. + * Wake up the zthr if it is sleeping. If the thread has been cancelled + * or is in the process of being cancelled, this is a no-op. */ void zthr_wakeup(zthr_t *t) { - mutex_enter(&t->zthr_request_lock); mutex_enter(&t->zthr_state_lock); /* - * There are 4 states that we can find the zthr when issuing + * There are 5 states that we can find the zthr when issuing * this broadcast: * * [1] The common case of the thread being asleep, at which @@ -310,17 +325,19 @@ zthr_wakeup(zthr_t *t) * is basically a no-op. * [4] The thread was just created/resumed, in which case the * behavior is similar to [3]. + * [5] The thread is in the middle of being cancelled, which + * will be a no-op. */ cv_broadcast(&t->zthr_cv); mutex_exit(&t->zthr_state_lock); - mutex_exit(&t->zthr_request_lock); } /* * Sends a cancel request to the zthr and blocks until the zthr is * cancelled. If the zthr is not running (e.g. has been cancelled - * already), this is a no-op. + * already), this is a no-op. Note that this function should not be + * called from syncing context as it could deadlock with the zthr_func. */ void zthr_cancel(zthr_t *t) @@ -363,8 +380,9 @@ zthr_cancel(zthr_t *t) } /* - * Sends a resume request to the supplied zthr. If the zthr is - * already running this is a no-op. + * Sends a resume request to the supplied zthr. If the zthr is already + * running this is a no-op. Note that this function should not be + * called from syncing context as it could deadlock with the zthr_func. */ void zthr_resume(zthr_t *t) |