On Jan 3, 2013, at 6:26 PM, "Myklebust, Trond" <Trond.Myklebust@xxxxxxxxxx> wrote: > On Thu, 2013-01-03 at 18:11 -0500, Trond Myklebust wrote: >> On Thu, 2013-01-03 at 17:26 -0500, Tejun Heo wrote: >>> Ooh, BTW, there was a bug where workqueue code created a false >>> dependency between two work items. Workqueue currently considers two >>> work items to be the same if they're on the same address and won't >>> execute them concurrently - ie. it makes a work item which is queued >>> again while being executed wait for the previous execution to >>> complete. >>> >>> If a work function frees the work item, and then waits for an event >>> which should be performed by another work item and *that* work item >>> recycles the freed work item, it can create a false dependency loop. >>> There really is no reliable way to detect this short of verifying >>> every memory free. A patch is queued to make such occurrences less >>> likely (work functions should also match for two work items considered >>> the same), but if you're seeing this, the best thing to do is freeing >>> the work item at the end of the work function. >> >> That's interesting... I wonder if we may have been hitting that issue. >> >> From what I can see, we do actually free the write RPC task (and hence >> the work_struct) before we call the asynchronous unlink completion... >> >> Dros, can you see if reverting commit >> 324d003b0cd82151adbaecefef57b73f7959a469 + commit >> 168e4b39d1afb79a7e3ea6c3bb246b4c82c6bdb9 and then applying the attached >> patch also fixes the hang on a pristine 3.7.x kernel? > > Actually, we probably also need to look at rpc_free_task, so the > following patch, instead... Yes, this patch fixes the hang! Thank you for the explanation Tejun - that makes a lot of sense and explains the workqueue behavior that we were seeing. -dros-- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
