[PATCH] uml: Fix process exit race

tt-mode closes switch_pipes in exit_thread_tt and kills processes in
switch_to_tt, if the exit_state is EXIT_DEAD or EXIT_ZOMBIE.

In very rare cases the exiting process can be scheduled out after having set
exit_state and closed switch_pipes (from release_task it calls proc_pid_flush,
which might sleep).  If this process is to be restarted, UML failes in
switch_to_tt with:

   write of switch_pipe failed, err = 9

We fix this by closing switch_pipes not in exit_thread_tt, but later in
release_thread_tt.  Additionally, we set switch_pipe[0] = 0 after closing.
switch_to_tt must not kill "from" process depending on its exit_state, but
must kill it after release_thread was processed only, so it examines
switch_pipe[0] for its decision.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 0 insertions, 5 deletions

diff --git a/arch/um/kernel/skas/include/mode_kern-skas.h b/arch/um/kernel/skas/include/mode_kern-skas.h
index 94c564962378..e48490028111 100644
--- a/arch/um/kernel/skas/include/mode_kern-skas.h
+++ b/arch/um/kernel/skas/include/mode_kern-skas.h
@@ -18,7 +18,6 @@ extern int copy_thread_skas(int nr, unsigned long clone_flags,
                             unsigned long sp, unsigned long stack_top,
                             struct task_struct *p, struct pt_regs *regs);
 extern void release_thread_skas(struct task_struct *task);
-extern void exit_thread_skas(void);
 extern void initial_thread_cb_skas(void (*proc)(void *), void *arg);
 extern void init_idle_skas(void);
 extern void flush_tlb_kernel_range_skas(unsigned long start,
diff --git a/arch/um/kernel/skas/process_kern.c b/arch/um/kernel/skas/process_kern.c
index 5d096ea63b97..ab5d3271da0b 100644
--- a/arch/um/kernel/skas/process_kern.c
+++ b/arch/um/kernel/skas/process_kern.c
@@ -83,10 +83,6 @@ void release_thread_skas(struct task_struct *task)
 {
 }
 
-void exit_thread_skas(void)
-{
-}
-
 void fork_handler(int sig)
 {
         change_sig(SIGUSR1, 1);