Messages in this thread | | | Date | Wed, 3 Sep 2008 16:32:48 +0200 | From | Louis Rilling <> | Subject | Re: [PATCH 8/9] Introduce functions to restart a process |
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On Wed, Sep 03, 2008 at 02:57:55PM +0400, Andrey Mirkin wrote: > Functions to restart process, restore its state, fpu and registers are added. > > Signed-off-by: Andrey Mirkin <major@openvz.org> > --- > arch/x86/kernel/entry_32.S | 21 +++ > arch/x86/kernel/process_32.c | 3 + > cpt/Makefile | 3 +- > cpt/cpt.h | 2 + > cpt/restart.c | 2 +- > cpt/rst_process.c | 277 ++++++++++++++++++++++++++++++++++++++++++ > kernel/sched.c | 1 + > 7 files changed, 307 insertions(+), 2 deletions(-) > create mode 100644 cpt/rst_process.c > > diff --git a/arch/x86/kernel/entry_32.S b/arch/x86/kernel/entry_32.S > index 109792b..a4848a3 100644 > --- a/arch/x86/kernel/entry_32.S > +++ b/arch/x86/kernel/entry_32.S > @@ -225,6 +225,7 @@ ENTRY(ret_from_fork) > GET_THREAD_INFO(%ebp) > popl %eax > CFI_ADJUST_CFA_OFFSET -4 > +ret_from_fork_tail: > pushl $0x0202 # Reset kernel eflags > CFI_ADJUST_CFA_OFFSET 4 > popfl > @@ -233,6 +234,26 @@ ENTRY(ret_from_fork) > CFI_ENDPROC > END(ret_from_fork) > > +ENTRY(i386_ret_from_resume) > + CFI_STARTPROC > + pushl %eax > + CFI_ADJUST_CFA_OFFSET 4 > + call schedule_tail > + GET_THREAD_INFO(%ebp) > + popl %eax > + CFI_ADJUST_CFA_OFFSET -4 > + movl (%esp), %eax > + testl %eax, %eax > + jz 1f > + pushl %esp > + call *%eax > + addl $4, %esp > +1: > + addl $256, %esp
This space reserved for hooks deserves some explanations IMO. I partly know the reasons, since I have looked at OpenVZ code with you, but I'm sure that almost nobody knows...
Btw, the constant HOOK_RESERVE should be defined in a common place for assembly and C as well.
> + jmp ret_from_fork_tail > + CFI_ENDPROC > +END(i386_ret_from_resume) > + > /* > * Return to user mode is not as complex as all this looks, > * but we want the default path for a system call return to
[...]
> diff --git a/cpt/rst_process.c b/cpt/rst_process.c > new file mode 100644 > index 0000000..6d47f3c > --- /dev/null > +++ b/cpt/rst_process.c > @@ -0,0 +1,277 @@ > +/* > + * Copyright (C) 2008 Parallels, Inc. > + * > + * Author: Andrey Mirkin <major@openvz.org> > + * > + * This program is free software; you can redistribute it and/or > + * modify it under the terms of the GNU General Public License as > + * published by the Free Software Foundation, version 2 of the > + * License. > + * > + */ > + > +#include <linux/sched.h> > +#include <linux/fs.h> > +#include <linux/file.h> > +#include <linux/version.h> > +#include <linux/module.h> > + > +#include "cpt.h" > +#include "cpt_image.h" > + > +#define HOOK_RESERVE 256 > + > +struct thr_context { > + struct completion complete; > + int error; > + struct cpt_context *ctx; > + struct task_struct *tsk; > +}; > + > +int local_kernel_thread(int (*fn)(void *), void * arg, unsigned long flags, pid_t pid) > +{ > + pid_t ret; > + > + if (current->fs == NULL) { > + /* do_fork_pid() hates processes without fs, oopses. */ > + eprintk("local_kernel_thread: current->fs==NULL\n"); > + return -EINVAL; > + } > + if (!try_module_get(THIS_MODULE)) > + return -EBUSY;
Doing try_module_get(THIS_MODULE) and checking its result is almost always the symptom of a BUG. I explain myself: If it is possible that THIS_MODULE is currently unloading, its memory (especially its text section) can be freed at any time during the call to local_kernel_thread(), which leads to a beautiful OOPS.
So, either the code is buggy, or this check is useless. I agree however that the module ref count must be incremented, since the new thread will run code from it.
> + ret = kernel_thread(fn, arg, flags); > + if (ret < 0) > + module_put(THIS_MODULE); > + return ret; > +} > + > +static unsigned int decode_task_flags(unsigned int task_flags) > +{ > + unsigned int flags = 0; > + > + if (task_flags & (1 << CPT_PF_EXITING)) > + flags |= PF_EXITING; > + if (task_flags & (1 << CPT_PF_FORKNOEXEC)) > + flags |= PF_FORKNOEXEC; > + if (task_flags & (1 << CPT_PF_SUPERPRIV)) > + flags |= PF_SUPERPRIV; > + if (task_flags & (1 << CPT_PF_DUMPCORE)) > + flags |= PF_DUMPCORE; > + if (task_flags & (1 << CPT_PF_SIGNALED)) > + flags |= PF_SIGNALED; > + > + return flags; > + > +} > + > +int rst_restore_task_struct(struct task_struct *tsk, struct cpt_task_image *ti, > + struct cpt_context *ctx) > +{ > + int i; > + > + /* Restore only saved flags, comm and tls for now */ > + tsk->flags = decode_task_flags(ti->cpt_flags); > + clear_tsk_thread_flag(tsk, TIF_FREEZE); > + memcpy(tsk->comm, ti->cpt_comm, TASK_COMM_LEN); > + for (i = 0; i < GDT_ENTRY_TLS_ENTRIES; i++) { > + tsk->thread.tls_array[i].a = ti->cpt_tls[i] & 0xFFFFFFFF; > + tsk->thread.tls_array[i].b = ti->cpt_tls[i] >> 32; > + } > + > + return 0; > +} > + > +static int rst_restore_fpustate(struct task_struct *tsk, struct cpt_task_image *ti, > + struct cpt_context *ctx) > +{ > + struct cpt_obj_bits hdr; > + int err; > + char *buf; > + > + clear_stopped_child_used_math(tsk); > + > + err = rst_get_object(CPT_OBJ_BITS, &hdr, sizeof(hdr), ctx); > + if (err < 0) > + return err; > + > + buf = kmalloc(hdr.cpt_size, GFP_KERNEL); > + if (!buf) > + return -ENOMEM; > + > + err = ctx->read(buf, hdr.cpt_size, ctx); > + if (err) > + goto out; > + > + if (hdr.cpt_content == CPT_CONTENT_X86_FPUSTATE && cpu_has_fxsr) { > + memcpy(&tsk->thread.xstate, buf, > + sizeof(struct i387_fxsave_struct)); > + if (ti->cpt_flags & CPT_PF_USED_MATH) > + set_stopped_child_used_math(tsk); > + } > +#ifndef CONFIG_X86_64 > + else if (hdr.cpt_content == CPT_CONTENT_X86_FPUSTATE_OLD && > + !cpu_has_fxsr) { > + memcpy(&tsk->thread.xstate, buf, > + sizeof(struct i387_fsave_struct)); > + if (ti->cpt_flags & CPT_PF_USED_MATH) > + set_stopped_child_used_math(tsk); > + } > +#endif > + > +out: > + kfree(buf); > + return err; > +} > + > +static u32 decode_segment(u32 segid) > +{ > + if (segid == CPT_SEG_ZERO) > + return 0; > + > + /* TLS descriptors */ > + if (segid <= CPT_SEG_TLS3) > + return ((GDT_ENTRY_TLS_MIN + segid - CPT_SEG_TLS1) << 3) + 3; > + > + /* LDT descriptor, it is just an index to LDT array */ > + if (segid >= CPT_SEG_LDT) > + return ((segid - CPT_SEG_LDT) << 3) | 7; > + > + /* Check for one of standard descriptors */ > + if (segid == CPT_SEG_USER32_DS) > + return __USER_DS; > + if (segid == CPT_SEG_USER32_CS) > + return __USER_CS; > + > + eprintk("Invalid segment reg %d\n", segid); > + return 0; > +} > + > +static int rst_restore_registers(struct task_struct *tsk, struct cpt_context *ctx) > +{ > + struct cpt_x86_regs ri; > + struct pt_regs *regs = task_pt_regs(tsk); > + extern char i386_ret_from_resume; > + int err; > + > + err = rst_get_object(CPT_OBJ_X86_REGS, &ri, sizeof(ri), ctx); > + if (err < 0) > + return err; > + > + tsk->thread.sp = (unsigned long) regs; > + tsk->thread.sp0 = (unsigned long) (regs+1); > + tsk->thread.ip = (unsigned long) &i386_ret_from_resume; > + > + tsk->thread.gs = decode_segment(ri.cpt_gs); > + tsk->thread.debugreg0 = ri.cpt_debugreg[0]; > + tsk->thread.debugreg1 = ri.cpt_debugreg[1]; > + tsk->thread.debugreg2 = ri.cpt_debugreg[2]; > + tsk->thread.debugreg3 = ri.cpt_debugreg[3]; > + tsk->thread.debugreg6 = ri.cpt_debugreg[6]; > + tsk->thread.debugreg7 = ri.cpt_debugreg[7]; > + > + regs->bx = ri.cpt_bx; > + regs->cx = ri.cpt_cx; > + regs->dx = ri.cpt_dx; > + regs->si = ri.cpt_si; > + regs->di = ri.cpt_di; > + regs->bp = ri.cpt_bp; > + regs->ax = ri.cpt_ax; > + regs->orig_ax = ri.cpt_orig_ax; > + regs->ip = ri.cpt_ip; > + regs->flags = ri.cpt_flags; > + regs->sp = ri.cpt_sp; > + > + regs->cs = decode_segment(ri.cpt_cs); > + regs->ss = decode_segment(ri.cpt_ss); > + regs->ds = decode_segment(ri.cpt_ds); > + regs->es = decode_segment(ri.cpt_es); > + regs->fs = decode_segment(ri.cpt_fs); > + > + tsk->thread.sp -= HOOK_RESERVE; > + memset((void*)tsk->thread.sp, 0, HOOK_RESERVE); > + > + return 0; > +} > + > +static int restart_thread(void *arg) > +{ > + struct thr_context *thr_ctx = arg; > + struct cpt_context *ctx; > + struct cpt_task_image *ti; > + int err; > + > + current->state = TASK_UNINTERRUPTIBLE; > + > + ctx = thr_ctx->ctx; > + ti = kmalloc(sizeof(*ti), GFP_KERNEL); > + if (!ti) > + return -ENOMEM; > + > + err = rst_get_object(CPT_OBJ_TASK, ti, sizeof(*ti), ctx); > + if (!err) > + err = rst_restore_task_struct(current, ti, ctx); > + /* Restore mm here */ > + if (!err) > + err = rst_restore_fpustate(current, ti, ctx); > + if (!err) > + err = rst_restore_registers(current, ctx); > + > + thr_ctx->error = err; > + complete(&thr_ctx->complete); > + > + if (!err && (ti->cpt_state & (EXIT_ZOMBIE|EXIT_DEAD))) { > + do_exit(ti->cpt_exit_code); > + } else { > + __set_current_state(TASK_UNINTERRUPTIBLE); > + } > + > + kfree(ti); > + schedule(); > + > + eprintk("leaked %d/%d %p\n", task_pid_nr(current), task_pid_vnr(current), current->mm); > + > + module_put(THIS_MODULE);
Where is the module ref count dropped in case of success?
> + complete_and_exit(NULL, 0); > + return 0; > +} > +static int create_root_task(struct cpt_context *ctx, > + struct thr_context *thr_ctx) > +{ > + struct task_struct *tsk; > + int pid; > + > + thr_ctx->ctx = ctx; > + thr_ctx->error = 0; > + init_completion(&thr_ctx->complete); > + > + /* We should also create container here */ > + pid = local_kernel_thread(restart_thread, thr_ctx, > + CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC | > + CLONE_NEWUSER | CLONE_NEWPID | CLONE_NEWNET, 0); > + if (pid < 0) > + return pid; > + read_lock(&tasklist_lock); > + tsk = find_task_by_vpid(pid); > + if (tsk) > + get_task_struct(tsk); > + read_unlock(&tasklist_lock); > + if (tsk == NULL) > + return -ESRCH; > + thr_ctx->tsk = tsk; > + return 0; > +} > + > +int rst_restart_process(struct cpt_context *ctx) > +{ > + struct thr_context thr_ctx_root; > + int err; > + > + err = create_root_task(ctx, &thr_ctx_root); > + if (err) > + return err; > + > + wait_for_completion(&thr_ctx_root.complete); > + wait_task_inactive(thr_ctx_root.tsk, 0);
I don't see the point of this two-steps completion. Could you explain?
Thanks,
Louis
-- Dr Louis Rilling Kerlabs Skype: louis.rilling Batiment Germanium Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes http://www.kerlabs.com/ 35700 Rennes [unhandled content-type:application/pgp-signature] | |