Messages in this thread Patch in this message | | | Date | Wed, 30 Jul 2008 13:09:21 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: 2.6.27-rc1: IP: iov_iter_advance+0x2e/0x90 |
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On Wed, 30 Jul 2008, Alexey Dobriyan wrote: > > Steps to reproduce: > > # while true; do ./ftest03; done > > ftest03 from LTP 20080603
Hmm. The oops disassembles to
-12: 4c 8b 07 mov (%rdi),%r8 -9: 48 8b 4f 10 mov 0x10(%rdi),%rcx -5: 48 85 f6 test %rsi,%rsi -2: 75 17 jne 0x42 0: 49 83 78 08 00 cmpq $0x0,0x8(%r8) <--- 5: 75 07 jne 0xe 7: 48 83 7f 18 00 cmpq $0x0,0x18(%rdi) c: 75 09 jne 0x17
So it looks like we just overflowed %r8 to a new page and you presumably have DEBUG_PAGEALLOC on.
(And yes, I see in the oops that you do)
> RIP [<ffffffff8026190e>] iov_iter_advance+0x2e/0x90 > Call Trace: > [<ffffffff80263452>] generic_file_buffered_write+0x1e2/0x710 > [<ffffffff8040cfd0>] ? _spin_unlock+0x30/0x60 > [<ffffffff80263e0f>] __generic_file_aio_write_nolock+0x29f/0x450 > [<ffffffff80264026>] generic_file_aio_write+0x66/0xd0 > [<ffffffff802c9506>] ext3_file_write+0x26/0xc0 > [<ffffffff80264250>] ? generic_file_aio_read+0x0/0x670 > [<ffffffff802c94e0>] ? ext3_file_write+0x0/0xc0 > [<ffffffff8028921b>] do_sync_readv_writev+0xeb/0x130 > [<ffffffff8025284d>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff802449c0>] ? autoremove_wake_function+0x0/0x40 > [<ffffffff80289055>] ? rw_copy_check_uvector+0x95/0x130 > [<ffffffff80289953>] do_readv_writev+0xc3/0x120 > [<ffffffff8025284d>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff802527b5>] ? trace_hardirqs_on_caller+0xd5/0x160 > [<ffffffff8025284d>] ? trace_hardirqs_on+0xd/0x10 > [<ffffffff802899e9>] vfs_writev+0x39/0x60 > [<ffffffff80289d60>] sys_writev+0x50/0x90 > [<ffffffff8020b65b>] system_call_fastpath+0x16/0x1b > > 0xffffffff8026190e is in iov_iter_advance (mm/filemap.c:1882). > 1877 > 1878 /* > 1879 * The !iov->iov_len check ensures we skip over unlikely > 1880 * zero-length segments (without overruning the iovec). > 1881 */ > 1882 ===> while (bytes || unlikely(!iov->iov_len && i->count)) {
And yes, that oopsing op would be the one that loads 'iov->iov_len'.
So it very much looks like iov_iter_advance() advances past the end of the iov array. We've had issues like that before. And I bet it's due to a combination of Nick's commit f7009264c519603b8ec67c881bd368a56703cfc9 ("iov_iter_advance() fix") and 124d3b7041f9a0ca7c43a6293e1cae4576c32fd5 ("fix writev regression: pan hanging unkillable and un-straceable").
It's simply _not_ acceptable to look at iov->iov_len when 'bytes' has gone down to zero, because there may be no 'iov' left!
Nick?
That said, I do think that we have another issue with iovec's - I think we should strive to always pass in the number of iovec's when we pass a pointer to an iovec, in addition to the bytes. The sad part is that 'iov_iter_advance' actually -has- the count, but it's the byte count remaining, not the iovec's remaining.
In this particular case, the trivial fix _may_ be to just change the order of testing iov->iov_len && i->count, but I really think we should also count actual iov entries and pass them around (and keep them updated).
So does this (hacky, ugly) patch fix it for you?
Linus
--- mm/filemap.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/mm/filemap.c b/mm/filemap.c index 42bbc69..d97d1ad 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1879,7 +1879,7 @@ void iov_iter_advance(struct iov_iter *i, size_t bytes) * The !iov->iov_len check ensures we skip over unlikely * zero-length segments (without overruning the iovec). */ - while (bytes || unlikely(!iov->iov_len && i->count)) { + while (bytes || unlikely(i->count && !iov->iov_len)) { int copy; copy = min(bytes, iov->iov_len - base);
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