Re: [kvm-devel] [GIT PULL][RESEND] Late KVM Updates for the 2.6.23 merge window

Linus Torvalds wrote:
On Sat, 21 Jul 2007, S.Çağlar Onur wrote:

With Linus's latest git, shutting down a guest (fired with -smp 2 -m 512) sometimes
ends up like [1], this occured as soon as qemu window closed.

[1] http://cekirdek.pardus.org.tr/~caglar/kvm/dmesg.latest


[ 737.460654] Bad page state in process 'qemu-kvm'
[ 737.460656] page:f5e68000 flags:0xea020000 mapping:00000000 mapcount:2 count:0
[ 737.460657] Trying to fix it up, but a reboot is needed
[ 737.460659] Backtrace:
[ 737.460691] [<c0159e70>] bad_page+0x64/0x8e
[ 737.460733] [<c015a7ee>] free_hot_cold_page+0x68/0x15a

That's the "free_pages_check()", and in particular it seems to be
"page_mapcount()" being non-zero that triggered that thing.

So it looks like something in KVM isn't coherent about the mapping vs the
usage counters..



Far more prosaic. It calls __free_page() on the cleanup path with the
page's virtual address instead of the struct page. I guess
__free_page() is happy with a zeroed out blob, which is the most likely
contents.

Trivial patch shortly.

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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