From: Bodo Stroesser Date: Sat, 7 May 2005 04:30:54 +0000 (-0700) Subject: [PATCH] uml: Fix process exit race X-Git-Tag: v2.6.12-rc4~2 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=0f7e663dea7f0e22f3b2d07156c5e9d2e8656610;p=linux-2.6 [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 Signed-off-by: Jeff Dike Cc: Paolo 'Blaisorblade' Giarrusso Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/arch/um/kernel/process_kern.c b/arch/um/kernel/process_kern.c index 3dcb080c44..c1adf7ba3f 100644 --- a/arch/um/kernel/process_kern.c +++ b/arch/um/kernel/process_kern.c @@ -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); } diff --git a/arch/um/kernel/skas/include/mode_kern-skas.h b/arch/um/kernel/skas/include/mode_kern-skas.h index 94c5649623..e484900281 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 5d096ea63b..ab5d3271da 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); diff --git a/arch/um/kernel/tt/include/mode_kern-tt.h b/arch/um/kernel/tt/include/mode_kern-tt.h index 28aaab3448..e0ca0e0b25 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 @@ 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); diff --git a/arch/um/kernel/tt/process_kern.c b/arch/um/kernel/tt/process_kern.c index f19f7c18fe..df810ca8fc 100644 --- a/arch/um/kernel/tt/process_kern.c +++ b/arch/um/kernel/tt/process_kern.c @@ -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)