> > > > From: Thomas Gleixner [mailto:tglx@xxxxxxxxxxxxx] > > > > > > > > I think I asked this before, but I might have missed the answer. > > > > > > > > Why is this a rw_sempahore? It's never taken with down_read and > > looking > > > > at the usage sites it's simply a mutex, right? > > > > > > If the semaphore --> mutex change would have been as simple as it > > sounds, > > > we would have had NO problem including it with the next version (v3) of > > this > > > patchset. But unfortunately, this change uncovered a latent defect, > which > > > necessitated yet another patch. (I know... hard to believe that > something > > > this simple would do that, but it did.) Rather than further complicating > > this > > > patchset, we thought it would be better to address the visorinput issues > > via a > > > separate follow-on patchset. > > > > That makes me curious. What's the issue? Functional is the mutex the > same > > thing as the r/w semaphore when the latter is only taken down_write and > > locked > > and released by the same thread, which is the case as far as I can tell. > > > > The issue: using it uninitialized (<blush>). > > A semaphore appears to let you get away with it, but a mutex does NOT. > We had to shuffle some things around to get this right. If you're > interested in a preview, you can find a patch in github at > https://github.com/davidker/unisys/commit/039e6e517b4a17e2d135a9df85 > cc1e24a39c2670. > The second bullet in that commit comment describes the scenario > where we were attempting to access the lock in visorinput_open() > before we had actually initialized it: > > * we canNOT get into visorinput_open() until the device > structure is totally initialized, by delaying the > input_register_device() until the end of device initialization > > I.e., before this patch, we WERE getting into visorinput_open() > during the call to input_register_device() that was done before > device initialization was complete, which was BEFORE we initialized > the semaphore. > > There is a 2nd follow-on patch that actually does the simple > semaphore --> mutex conversion at > https://github.com/davidker/unisys/commit/6f57ed62ae206c23c58ce4a016 > b08e15639ce9af. > > > > Is that acceptable for you? > > > > Please fix it before moving the drivers out of staging. > > Absolutely. We will probably push that patchset (containing the > 2 github patches referenced above) within the next few days, > even if this visorbus patchset hasn't moved. > The 2 patches referenced above (which include the bug fix, and the change from semaphore to mutex) are included as patches #27 and #28 in the patchset just submitted by David Kershner: [PATCH RESEND 00/28] staging: unisys: fix visorbus & visorinput issues raised by tglx Thanks. Tim Sell -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
