Messages in this thread | | | Date | Wed, 28 Jan 2009 12:58:38 -0500 | From | Masami Hiramatsu <> | Subject | Re: [BUG][kprobes][vunmap?]: kprobes may cause memory corruption |
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Mathieu Desnoyers wrote: > * Masami Hiramatsu (mhiramat@redhat.com) wrote: >> Mathieu Desnoyers wrote: [...] >>> All this called in a loop. This would help isolating the "vmap" part of >>> the issue. If this test is not enough, then we should maybe try >>> something like this in a kernel module (which does what text_poke does >>> with vmalloc, more or less) in a loop : >>> >>> char somedata[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE))); >>> char copydata[PAGE_SIZE] __attribute__((aligned(PAGE_SIZE))); >> Should both of them have PAGE_SIZE*2? >> > > Yes. > >>> void test_vmap(void) >>> } >>> struct page *pages[2]; >>> char *vaddr; >>> int i; >>> >>> for (i = 0; i < 2 * PAGE_SIZE; i++) >>> copydata[i] = somedata[i]; >>> page[0] = virt_to_page(&somedata); >>> BUG_ON(!page[0]); >>> page[1] = virt_to_page(&somedata + PAGE_SIZE); >>> BUG_ON(!page[1]);
Oops, these should be vmalloc_to_page(), shouldn't it?
>>> vaddr = vmap(pages, 2, VM_MAP, PAGE_KERNEL); >>> BUG_ON(!vaddr); >>> >>> for (i = 0; i < 2 * PAGE_SIZE; i++) >>> vaddr[i] = copydata[i] + 1; >>> >>> vunmap(vaddr); >>> >>> for (i = 0; i < 2 * PAGE_SIZE; i++) >>> BUG_ON(somedata[i] != copydata[i] + 1); >>> } >> Hmm, when I ran above code, it hit the last BUG_ON(). >> I checked that somedata[i] didn't updated. >> > > Do you hit the BUG_ON after the first loop ?
At the first loop, it hit the BUG_ON.
>>> Given you don't seem to have hit the >>> for (i = 0; i < len; i++) >>> BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]); >>> test at the end of text_poke, >> However, when I ran kprobe-based test, it doesn't hit the BUG_ON() >> in text_poke(). >> > > The variable declarations should have been 2*PAGE_SIZE, hopefully you > fixed them.
Sure,
> There is also a sync_core() in text_poke. It should not matter, but > maybe that could help ?
Adding sync_core() could not help me... anyway, I'll try again with using vmalloc_to_page().
>>> I suspect the write through the vmapped >>> area is correctly done, but that the problem may lay in the mm layer. >>> Maybe it's running out of pre-allocated vmap areas or something like >>> this ? >> I haven't seen vmalloc failure message on 2.6.29-rc2. >> > > It could be because the available vmalloc space is slightly higher. > Looking into the lazy vunmap threshold would be useful. > > You could also try with loop values higher than 400.
OK, Thanks,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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