[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>
diff --git a/arch/um/kernel/process_kern.c b/arch/um/kernel/process_kern.c
index 3dcb080..c1adf7b 100644
--- a/arch/um/kernel/process_kern.c
+++ b/arch/um/kernel/process_kern.c
@@ -142,7 +142,6 @@
void exit_thread(void)
{
- CHOOSE_MODE(exit_thread_tt(), exit_thread_skas());
unprotect_stack((unsigned long) current_thread);
}
diff --git a/arch/um/kernel/skas/include/mode_kern-skas.h b/arch/um/kernel/skas/include/mode_kern-skas.h
index 94c5649..e484900 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 @@
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 5d096ea..ab5d327 100644
--- a/arch/um/kernel/skas/process_kern.c
+++ b/arch/um/kernel/skas/process_kern.c
@@ -83,10 +83,6 @@
{
}
-void exit_thread_skas(void)
-{
-}
-
void fork_handler(int sig)
{
change_sig(SIGUSR1, 1);
diff --git a/arch/um/kernel/tt/include/mode_kern-tt.h b/arch/um/kernel/tt/include/mode_kern-tt.h
index 28aaab3..e0ca0e0 100644
--- a/arch/um/kernel/tt/include/mode_kern-tt.h
+++ b/arch/um/kernel/tt/include/mode_kern-tt.h
@@ -19,7 +19,6 @@
unsigned long stack_top, struct task_struct *p,
struct pt_regs *regs);
extern void release_thread_tt(struct task_struct *task);
-extern void exit_thread_tt(void);
extern void initial_thread_cb_tt(void (*proc)(void *), void *arg);
extern void init_idle_tt(void);
extern void flush_tlb_kernel_range_tt(unsigned long start, unsigned long end);
diff --git a/arch/um/kernel/tt/process_kern.c b/arch/um/kernel/tt/process_kern.c
index f19f7c1..df810ca 100644
--- a/arch/um/kernel/tt/process_kern.c
+++ b/arch/um/kernel/tt/process_kern.c
@@ -65,8 +65,7 @@
panic("write of switch_pipe failed, err = %d", -err);
reading = 1;
- if((from->exit_state == EXIT_ZOMBIE) ||
- (from->exit_state == EXIT_DEAD))
+ if(from->thread.mode.tt.switch_pipe[0] == -1)
os_kill_process(os_getpid(), 0);
err = os_read_file(from->thread.mode.tt.switch_pipe[0], &c, sizeof(c));
@@ -81,8 +80,7 @@
* in case it has not already killed itself.
*/
prev_sched = current->thread.prev_sched;
- if((prev_sched->exit_state == EXIT_ZOMBIE) ||
- (prev_sched->exit_state == EXIT_DEAD))
+ if(prev_sched->thread.mode.tt.switch_pipe[0] == -1)
os_kill_process(prev_sched->thread.mode.tt.extern_pid, 1);
change_sig(SIGVTALRM, vtalrm);
@@ -101,14 +99,18 @@
{
int pid = task->thread.mode.tt.extern_pid;
+ /*
+ * We first have to kill the other process, before
+ * closing its switch_pipe. Else it might wake up
+ * and receive "EOF" before we could kill it.
+ */
if(os_getpid() != pid)
os_kill_process(pid, 0);
-}
-void exit_thread_tt(void)
-{
- os_close_file(current->thread.mode.tt.switch_pipe[0]);
- os_close_file(current->thread.mode.tt.switch_pipe[1]);
+ os_close_file(task->thread.mode.tt.switch_pipe[0]);
+ os_close_file(task->thread.mode.tt.switch_pipe[1]);
+ /* use switch_pipe as flag: thread is released */
+ task->thread.mode.tt.switch_pipe[0] = -1;
}
void suspend_new_thread(int fd)
