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[PATCH] uml: Fix process exit race

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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>
This commit is contained in:
Bodo Stroesser 2005-05-06 21:30:54 -07:00 committed by Linus Torvalds
parent b8bd0220c1
commit 0f7e663dea
5 changed files with 11 additions and 16 deletions
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1
arch/um/kernel/process_kern.c
View File

@ -142,7 +142,6 @@ void release_thread(struct task_struct *task)
void exit_thread(void)
{
CHOOSE_MODE(exit_thread_tt(), exit_thread_skas());
unprotect_stack((unsigned long) current_thread);
}

1
arch/um/kernel/skas/include/mode_kern-skas.h
View File

@ -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,

4
arch/um/kernel/skas/process_kern.c
View File

@ -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);

1
arch/um/kernel/tt/include/mode_kern-tt.h
View File

@ -19,7 +19,6 @@ extern int copy_thread_tt(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_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);

20
arch/um/kernel/tt/process_kern.c
View File

@ -65,8 +65,7 @@ void *switch_to_tt(void *prev, void *next, void *last)
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 @@ void *switch_to_tt(void *prev, void *next, void *last)
* 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 @@ void release_thread_tt(struct task_struct *task)
{
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)