Messages in this thread | | | Date | Wed, 28 Jan 2009 11:59:27 -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: >> Masami Hiramatsu wrote: > Hi Masami, > > This would not surprise me if it came from bug in the new vmap() > implementation done in this commit : > > http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=db64fe02258f1507e13fe5212a989922323685ce > > Especially because going from vmap -> vm_map_ram makes this behavior > disappear. > > Looking at the commit, I notice that it delays vunmap so it's done in > batch to minimize locking effect. I think it would be good to create a > test case to try to isolate this, without any kprobes/text_poke > involved, which does something like this : > > load module (this is also doing vmalloc, so it might be part of the > problem) > for i (i=0; i < 400; i++) { > vmap() > vfree() ^^^^^ vunmap? > } > unload module > > Another interesting test would be : > > for i (i=0; i < 400; i++) { > vmalloc() > vfree() > }
Hi Mathieu,
Thank you for test ideas. I made both of above two tests and run it. Both test modules do NOT cause memory corruption...
> 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?
> > 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]); > 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.
> 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().
> 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.
Thank you again,
-- Masami Hiramatsu
Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division
e-mail: mhiramat@redhat.com
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