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SubjectRe: [PATCH] procfs task exe symlink
On Wed, 06 Feb 2008 17:44:29 -0800 Matt Helsley <matthltc@us.ibm.com> wrote:

> The kernel implements readlink of /proc/pid/exe by getting the file from the
> first executable VMA. Then the path to the file is reconstructed and reported as
> the result.
>
> Because of the VMA walk the code is slightly different on nommu systems. This
> patch avoids separate /proc/pid/exe code on nommu systems. Instead of walking
> the VMAs to find the first executable file-backed VMA we store a reference to
> the exec'd file in the mm_struct.
>
> That reference would prevent the filesystem holding the executable file from
> being unmounted even after unmapping the VMAs. So we track the number of
> VM_EXECUTABLE VMAs and drop the new reference when the last one is unmapped.
> This avoids pinning the mounted filesystem.
>
> Andrew, these are the updates I promised. Please consider this patch for
> inclusion in -mm.
>

A hitherto-unsuspected patch has been instasnuck into mainline:


commit 3b1253880b7a9e6db54b943b2d40bcf2202f58ab
Author: Al Viro <viro@zeniv.linux.org.uk>
Date: Tue Apr 22 05:31:30 2008 -0400

[PATCH] sanitize unshare_files/reset_files_struct



which presented me with this:

***************
*** 963,968 ****
retval = unshare_files();
if (retval)
goto out;
/*
* Release all of the old mmap stuff
*/
--- 963,971 ----
retval = unshare_files();
if (retval)
goto out;
+
+ set_mm_exe_file(bprm->mm, bprm->file);
+
/*
* Release all of the old mmap stuff
*/


Which I fixed by simply doing:

--- a/fs/exec.c~procfs-task-exe-symlink
+++ a/fs/exec.c
@@ -954,6 +954,8 @@ int flush_old_exec(struct linux_binprm *
if (retval)
goto out;

+ set_mm_exe_file(bprm->mm, bprm->file);
+
/*
* Release all of the old mmap stuff
*/
However I'd ask that you conform that this is OK. If set_mm_exe_file() is
independent of unshare_files() then we're OK. If however there is some
ordering dependency then we'll need to confirm that the present ordering of the
unshare_files() and set_mm_exe_file() is correct.

Thanks.




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