On Wed, 2007-05-30 at 13:09 -0500, Serge E. Hallyn wrote:
> Quoting Matt Helsley ([EMAIL PROTECTED]):
> > This patch avoids holding the mmap semaphore while walking VMAs in response
> > to
> > programs which read or follow the /proc/<pid|self>/exe symlink. This also
> > allows us
> > to merge mmu and nommu proc_exe_link() functions. The costs are holding a
> > separate
> > reference to the executable file stored in the task struct and increased
> > code in
> > fork, exec, and exit paths.
> >
> > Signed-off-by: Matt Helsley <[EMAIL PROTECTED]>
> > ---
> >
> > Compiled and passed simple tests for regressions when patched against a
> > 2.6.20
> > and 2.6.22-rc2-mm1 kernel.
> >
> > fs/exec.c | 5 +++--
> > fs/proc/base.c | 20 ++++++++++++++++++++
> > fs/proc/internal.h | 1 -
> > fs/proc/task_mmu.c | 34 ----------------------------------
> > fs/proc/task_nommu.c | 34 ----------------------------------
> > include/linux/sched.h | 1 +
> > kernel/exit.c | 2 ++
> > kernel/fork.c | 10 +++++++++-
> > 8 files changed, 35 insertions(+), 72 deletions(-)
<snip>
> > Index: linux-2.6.22-rc2-mm1/kernel/exit.c
> > ===================================================================
> > --- linux-2.6.22-rc2-mm1.orig/kernel/exit.c
> > +++ linux-2.6.22-rc2-mm1/kernel/exit.c
> > @@ -924,10 +924,12 @@ fastcall void do_exit(long code)
> > if (unlikely(tsk->audit_context))
> > audit_free(tsk);
> >
> > taskstats_exit(tsk, group_dead);
> >
> > + if (tsk->exe_file)
> > + fput(tsk->exe_file);
>
> Hi,
>
> just taking a cursory look so I may be missing something, but doesn't
> this leave the possibility that right here, with tsk->exe_file being
> put, another task would try to look at tsk's /proc/tsk->pid/exe?
>
> thanks,
> -serge
>
> exit_mm(tsk);
>
<snip>
Good question. To be precise, I think the problem doesn't exist here but
after the exit_mm() because there's a VMA that holds a reference to the
same file.
The existing code appears to solve the race between
reading/following /proc/tsk->pid/exe and exit_mm() in the exit path by
returning -ENOENT for the case where there is no executable VMA with a
reference to the file backing it.
So I need to put NULL in the exe_file field and adjust the return value
to be -ENOENT instead of -ENOSYS.
Thanks for the review!
Cheers,
-Matt Helsley
-
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