[Devel] Re: ckpt-v19-rc2

[Nathan Lynch]

On Wed, 2009-12-02 at 00:23 -0500, Oren Laadan wrote:
> I put together ckpt-v19-rc2 (kernel and user)

I'm not sure yet whether this is a regression, but checkpoint seems to
be unable to handle file mappings that extend past the end of the file.
I noticed this with Fedora 11 userspace on powerpc (ld.so sometimes maps
libraries this way).  I did not see this failure with a v19-rc1-based
kernel I tested earlier this week, but I haven't retested with that yet.

Here's an example - 8K mapping of a 4K file:

# stat -c%s /tmp/myfile 
4096

# grep myfile /proc/5164/maps
f7e2b000-f7e2d000 r--p 00000000 08:06 5103709                            /tmp/myfile

# checkpoint 5164 > /tmp/mmap.ckpt
checkpoint: Bad address

When we try to follow the mapping past the end of the file, we get
VM_FAULT_SIGBUS from handle_mm_fault(); the stack trace from debugging
code I added is:

.__get_dirty_page+0x4c/0x164 (unreliable)
.checkpoint_memory_contents+0x134/0x5a4
.private_vma_checkpoint+0xf4/0x120
.filemap_checkpoint+0x198/0x1d0
.checkpoint_mm+0x3c4/0x4fc
.checkpoint_obj+0x17c/0x1d0
.checkpoint_obj_mm+0x50/0x88
.checkpoint_task+0x710/0xaa0
.do_checkpoint+0x9c0/0xb24
.SyS_checkpoint+0xd0/0x11c

Attached is a testcase.

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