Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261360AbVEFXwy (ORCPT ); Fri, 6 May 2005 19:52:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261315AbVEFXZG (ORCPT ); Fri, 6 May 2005 19:25:06 -0400 Received: from lakshmi.addtoit.com ([198.99.130.6]:48646 "EHLO lakshmi.solana.com") by vger.kernel.org with ESMTP id S261354AbVEFXOh (ORCPT ); Fri, 6 May 2005 19:14:37 -0400 Message-Id: <200505062249.j46Mnbpo010490@ccure.user-mode-linux.org> X-Mailer: exmh version 2.7.2 01/07/2005 with nmh-1.0.4 To: torvalds@osdl.org, akpm@osdl.org cc: linux-kernel@vger.kernel.org, user-mode-linux-devel@lists.sourceforge.net, Bodo Stroesser Subject: [PATCH 11/12] UML - Fix process exit race Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Date: Fri, 06 May 2005 18:49:37 -0400 From: Jeff Dike Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5282 Lines: 126 From: Bodo Stroesser 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 Index: linux-2.6.12-rc3-mm/arch/um/kernel/process_kern.c =================================================================== --- linux-2.6.12-rc3-mm.orig/arch/um/kernel/process_kern.c 2005-05-06 14:52:11.000000000 -0400 +++ linux-2.6.12-rc3-mm/arch/um/kernel/process_kern.c 2005-05-06 14:53:03.000000000 -0400 @@ -143,7 +143,6 @@ void exit_thread(void) { - CHOOSE_MODE(exit_thread_tt(), exit_thread_skas()); unprotect_stack((unsigned long) current_thread); } Index: linux-2.6.12-rc3-mm/arch/um/kernel/skas/include/mode_kern-skas.h =================================================================== --- linux-2.6.12-rc3-mm.orig/arch/um/kernel/skas/include/mode_kern-skas.h 2005-05-06 14:35:08.000000000 -0400 +++ linux-2.6.12-rc3-mm/arch/um/kernel/skas/include/mode_kern-skas.h 2005-05-06 14:53:03.000000000 -0400 @@ -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, Index: linux-2.6.12-rc3-mm/arch/um/kernel/skas/process_kern.c =================================================================== --- linux-2.6.12-rc3-mm.orig/arch/um/kernel/skas/process_kern.c 2005-05-06 14:35:08.000000000 -0400 +++ linux-2.6.12-rc3-mm/arch/um/kernel/skas/process_kern.c 2005-05-06 14:53:03.000000000 -0400 @@ -83,10 +83,6 @@ { } -void exit_thread_skas(void) -{ -} - void fork_handler(int sig) { change_sig(SIGUSR1, 1); Index: linux-2.6.12-rc3-mm/arch/um/kernel/tt/include/mode_kern-tt.h =================================================================== --- linux-2.6.12-rc3-mm.orig/arch/um/kernel/tt/include/mode_kern-tt.h 2005-05-06 14:35:08.000000000 -0400 +++ linux-2.6.12-rc3-mm/arch/um/kernel/tt/include/mode_kern-tt.h 2005-05-06 14:53:03.000000000 -0400 @@ -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); Index: linux-2.6.12-rc3-mm/arch/um/kernel/tt/process_kern.c =================================================================== --- linux-2.6.12-rc3-mm.orig/arch/um/kernel/tt/process_kern.c 2005-05-06 14:35:08.000000000 -0400 +++ linux-2.6.12-rc3-mm/arch/um/kernel/tt/process_kern.c 2005-05-06 14:54:39.000000000 -0400 @@ -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) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/