Messages in this thread | | | Date | Sun, 23 Nov 2014 16:03:06 -0500 | From | Rik van Riel <> | Subject | Re: [PATCH] ipc,sem block sem_lock on sma->lock during sma initialization |
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On 11/23/2014 01:23 PM, Manfred Spraul wrote: > Hi Rik, > > On 11/21/2014 08:52 PM, Rik van Riel wrote: >> When manipulating just one semaphore with semop, sem_lock only >> takes that single semaphore's lock. This creates a problem during >> initialization of the semaphore array, when the data structures >> used by sem_lock have not been set up yet. The sma->lock is >> already held by newary, and we just have to make sure everything >> else waits on that lock during initialization. >> >> Luckily it is easy to make sem_lock wait on the sma->lock, by >> pretending there is a complex operation in progress while the sma >> is being initialized. > That's not sufficient, as sma->sem_nsems is accessed before > calling sem_lock(), both within find_alloc_undo() and within > semtimedop(). > > The root problem is that sma->sem_nsems and sma->sem_base are > accessed without any locks, this conflicts with the approach that > sma starts to exist as not yet initialized but locked and is > unlocked after the initialization is completed. > > Attached is an idea. It did pass a few short tests. What do you > think?
This was my other idea for fixing the issue; unfortunately I didn't think of it until after I sent the first patch :)
You are right that without that change, we can return the wrong error codes to userspace.
I will give the patch a try, though I have so far been unable to reproduce the bug that the customer reported, so I am unlikely to give much in the way of useful testing results...
Andrew, feel free to give Manfred's patch my
Acked-by: Rik van Riel <riel@redhat.com>
It closes off more things than my patch did, in a similar way (doing something before ipc_addid)
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