Messages in this thread | | | Date | Fri, 5 Nov 2004 12:17:51 +0100 | From | Andi Kleen <> | Subject | Re: 2.6.10-rc1-mm3 |
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On Fri, Nov 05, 2004 at 12:09:51PM +0100, Ingo Molnar wrote: > > * Ingo Molnar <mingo@elte.hu> wrote: > > > > ------------[ cut here ]------------ > > > kernel BUG at mm/memory.c:156! > > > > > Process shmt04 (pid: 4854, threadinfo=dca51000 task=de374510) > > > > reproducible here too, just running LTP's shmt04 directly triggers it > > immediately. Looks like there's interaction of 4-level pagetables with > > ipc/shm.c or mm/shmem.c. > > due to the PML4 feature, the clear_page_tables() function changed to > clear_page_range(), changing its (first,size) argument to (first,last). > Normally it's called with (0,TASK_SIZE) which normally is PML4-aligned, > but in the (relatively rare) do_munmap() use this is not the case. We > correctly calculate the range that could be cleared, but it's not > PML4_SIZE aligned.
I think just removing the BUG_ON is easier. I sent a patch for that to Andrew.
> The solution is to clip both 'first' and 'last' to PML4_SIZE boundary. > Since when we calculate 'first' we add at least +PML4_SIZE to the value, > it is safe to clip 'first'. It is obviously safe to clip 'last'.
It's a bit tricky because on 3level architectures it clips on PGDs, not PML4s, otherwise it would never free any pagetables. But the if()s check that correctly.
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