Messages in this thread | | | Date | Mon, 29 Sep 2014 21:27:09 -0700 | Subject | Re: pipe/page fault oddness. | From | Linus Torvalds <> |
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On Mon, Sep 29, 2014 at 8:33 PM, Dave Jones <davej@redhat.com> wrote: > > Looking at the dump, there's only one running trinity child, > with all the others blocking on it. > > trinity-c49 R running task 12856 19464 7633 0x00000004 > ffff8800a09bf960 0000000000000002 ffff8800a09bf9f8 ffff880219650000 > 00000000001d4080 0000000000000000 ffff8800a09bffd8 00000000001d4080 > ffff88023f755bc0 ffff880219650000 ffff8800a09bffd8 ffff88010b017e00 > Call Trace: > [<ffffffff911c3c67>] handle_mm_fault+0x3a7/0xcd0 > [<ffffffff91042c84>] __do_page_fault+0x1a4/0x600 > [<ffffffff910430fe>] do_page_fault+0x1e/0x70 > [<ffffffff918264b2>] page_fault+0x22/0x30 > [<ffffffff911bd7e3>] ? copy_page_to_iter+0x3b3/0x500 > [<ffffffff9120eddf>] pipe_read+0xdf/0x330 > > Running the function tracer on that pid shows it spinning forever.. > http://codemonkey.org.uk/junk/pipe-trace.txt > > Kernel bug (missing EFAULT check somewhere perhaps?), or is this a > case where the fuzzer asked the kernel to do something stupid, and it obliged ?
Hmm. It looks like copy_page_to_iter_iovec() is broken and keeps not making any progress while just faulting.
I don't see how that could happen, though. All the loops there are conditional on the user copies *not* failing (ie "!left"), and they seem to properly update "iov".
Mind sending a disassembly of your "copy_page_to_iter" function, in particular around that whole "0x3b3/0x500" area which is where the page fault seems to happen?
Adding Al to the cc, since this code is from his commit 6e58e79db8a1 ("introduce copy_page_to_iter, kill loop over iovec in generic_file_aio_read()") but I don't see anything obviously wrong there.
Al? Do you see something I don't? Dave's function trace does seem to say that it doesn't even get back to pipe_read(), though, so the loop really must be inside copy_page_to_iter().
Linus
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