Messages in this thread | | | Date | Tue, 08 Aug 2006 19:54:19 +0400 | From | Kirill Korotaev <> | Subject | Re: [PATCH] sys_getppid oopses on debug kernel |
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>>>Accessing freed memory is a bug, always, not just *only* when slab >>>debugging is on, right? Doesn't this mean we could get junk, or that >>>the reader could potentially run off a bad pointer? >> >>no, read the comment in sys_getppid. >>It is a valid optimization. _safe_ and alowing to bypass taking the lock. >>BUT! This optimization relies on the fact that kernel memory (DMA + normal zone) >>is always mapped into virtual address space. >>Which is invalid for debug kernels only. > > > Actually, it might also be invalid in hypervisor environments. s390 and > Xen use ballooning drivers to tell the hypervisor which pages are not > currently in use by the OS so that they may be used in virtual machines > elsewhere. > > I'm cc'ing the s390 guys. Will the s390 kernel oops if it accesses a > page which was ballooned back to the hypervisor?
Yeah, a minute after my reply I got your idea and sent a new patch which always takes the lock :)))
Thanks, Kirill
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