Messages in this thread Patch in this message | | | Date | Tue, 24 Jul 2007 10:17:50 +0200 | From | Jens Axboe <> | Subject | Re: 2.6.23-rc1: BUG_ON in kmap_atomic_prot() |
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On Mon, Jul 23 2007, Andrew Morton wrote: > I worked out that the crash I saw was in > > BUG_ON(!pte_none(*(kmap_pte-idx))); > > in the read of kmap_pte[idx]. Which would be weird as the caller is using > a literal KM_USER0. > > So maybe I goofed, and that BUG_ON is triggering (it scrolled off, and I am > unable to reproduce it now). > > If that BUG_ON _is_ triggering then it might indicate that someone is doing > a __GFP_HIGHMEM|__GFP_ZERO allocation while holding KM_USER0.
Or doing double kunmaps, or doing a kunmap_atomic() on the page, not the address. I've seen both of those end up triggering that BUG_ON() in a later kmap.
Looking over the 2.6.22..2.6.23-rc1 diff, I found one such error in ocfs2 at least. But you are probably not using that, so I'll keep looking...
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[PATCH] ocfs2: bad kunmap_atomic()
kunmap_atomic() takes the virtual address, not the mapped page as argument.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c index 5727cd1..c4034f6 100644 --- a/fs/ocfs2/file.c +++ b/fs/ocfs2/file.c @@ -2153,7 +2153,7 @@ static int ocfs2_splice_write_actor(struct pipe_inode_info *pipe, src = buf->ops->map(pipe, buf, 1); dst = kmap_atomic(page, KM_USER1); memcpy(dst + offset, src + buf->offset, count); - kunmap_atomic(page, KM_USER1); + kunmap_atomic(dst, KM_USER1); buf->ops->unmap(pipe, buf, src); copied = ocfs2_write_end(file, file->f_mapping, sd->pos, count, count, -- Jens Axboe
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