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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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20
arch/um/kernel/tt/process_kern.c
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@@ -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)