Re: + c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-update-after-mm-num_exe_file_vmas-removal.patch added to -mm tree

From: Konstantin Khlebnikov
Date: Thu Apr 19 2012 - 17:47:07 EST

Oleg Nesterov wrote:
On 04/20, Cyrill Gorcunov wrote:

On Thu, Apr 19, 2012 at 09:20:05PM +0200, Oleg Nesterov wrote:
On 04/19, Andrew Morton wrote:

From: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>
Subject: c/r: prctl: update prctl_set_mm_exe_file() after mm->num_exe_file_vmas removal

[ fix for "c-r-prctl-add-ability-to-set-new-mm_struct-exe_file-v2" from mm tree ]

After removing mm->num_exe_file_vmas kernel keeps mm->exe_file until final
mmput(), it never becomes NULL while task is alive.

We can check for other mapped files in mm instead of checking
mm->num_exe_file_vmas, and mark mm with flag MMF_EXE_FILE_CHANGED in order
to forbid second changing of mm->exe_file.

I lost the track a long ago.

Just one question, what does this "forbid second changing" actually mean?

Heh :) Oleg, it was actually your idea to make this feature "one-shot".

Heh, no ;)

IIRC, I only asked you what do you actually want,

Just one note for the record, prctl_set_mm_exe_file() does

if (mm->num_exe_file_vmas)
return -EBUSY;

We could do

if (mm->exe_file)
return -EBUSY;

This way "because this feature is a special to C/R" becomes
really true. IOW, you can't do PR_SET_MM_EXE_FILE twice.

I am fine either way, just I want to ensure you really want
the current version.

and only because it was documented as "feature is a special to C/R".

Once exe-file changed to a new value, it can't be changed again. The
reason was to bring at least minimum disturbance in sysadmins life.

You misunderstood. I am not arguing with "one-shot", I do not really

My question is: unless I missed something "it can't be changed again"
is not actually true. A task does PR_SET_MM_EXE_FILE, then it forks
the new child. The child can do PR_SET_MM_EXE_FILE again. Is this
by design?


I found more weird case: child thread (with CLONE_THREAD and without CLONE_VM)
changes its exe_file...
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