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The taskq_t's active thread list is sorted based on its tqt_ent->tqent_id field. The list is kept sorted solely by inserting new taskq_thread_t's in their correct sorted location; no other means is used. This means that once inserted, if a taskq_thread_t's tqt_ent->tqent_id field changes, the list runs the risk of no longer being sorted. Prior to the introduction of the taskq_dispatch_prealloc() interface, this was not a problem as a taskq_ent_t actively being serviced under the old interface should always have a static tqent_id field. Thus, once the taskq_thread_t is added to the taskq_t's active thread list, the taskq_thread_t's tqt_ent->tqent_id field would remain constant. Now, this is no longer the case. Currently, if using the taskq_dispatch_prealloc() interface, any given taskq_ent_t actively being serviced _may_ have its tqent_id value incremented. This happens when the preallocated taskq_ent_t structure is recursively dispatched. Thus, a taskq_thread_t could potentially have its tqt_ent->tqent_id field silently modified from under its feet. If this were to happen to a taskq_thread_t on a taskq_t's active thread list, this would compromise the integrity of the order of the list (as the list _may_ no longer be sorted). To get around this, the taskq_thread_t's taskq_ent_t pointer was replaced with its own static copy of the tqent_id. So, as a taskq_ent_t is pulled off of the taskq_t's pending list, a static copy of its tqent_id is made and this copy is used to sort the active thread list. Using a static copy is key in ensuring the integrity of the order of the active thread list. Even if the underlying taskq_ent_t is recursively dispatched (as has its tqent_id modified), this static copy stored inside the taskq_thread_t will remain constant. Signed-off-by: Prakash Surya <surya1@llnl.gov> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Issue #71 |
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| .. | ||
| .gitignore | ||
| Makefile.in | ||
| spl-atomic.c | ||
| spl-condvar.c | ||
| spl-cred.c | ||
| spl-debug.c | ||
| spl-err.c | ||
| spl-generic.c | ||
| spl-kmem.c | ||
| spl-kobj.c | ||
| spl-kstat.c | ||
| spl-module.c | ||
| spl-mutex.c | ||
| spl-proc.c | ||
| spl-rwlock.c | ||
| spl-taskq.c | ||
| spl-thread.c | ||
| spl-time.c | ||
| spl-tsd.c | ||
| spl-vnode.c | ||
| spl-xdr.c | ||
| spl-zlib.c | ||