On Tue, 28 Feb 2012 13:04:23 +0400
Dmitry Antipov <dmitry.anti...@linaro.org> wrote:
> Debugging option CONFIG_MODULE_KTHREAD_CHECK provides a way to check
> whether all kernel threads created by the module and have used module
> code as a thread worker function are really exited when the module is
> unloaded. The following pseudo-code contains example of an error which
> is likely to be catched with this debugging check:
>
> static struct task_struct *tsk;
> static DECLARE_COMPLETION(done);
>
> static void *func(void *unused)
> {
> while (!kthread_should_stop())
> real_work();
> complete(&done);
> }
>
> static int __init modinit(void)
> {
> tsk = kthread_run(func, NULL, "func");
> return IS_ERR(tsk) ? PTR_ERR(tsk) : 0;
> }
>
> static void __exit modexit(void)
> {
> wait_for_completion(&done);
> }
Might be a little bit useful. But I don't recall us having this bug in
quite a long time.
> index 0714b24..33897c3 100644
> --- a/include/linux/kthread.h
> +++ b/include/linux/kthread.h
> @@ -13,6 +13,11 @@ struct task_struct *kthread_create_on_node(int
> (*threadfn)(void *data),
> #define kthread_create(threadfn, data, namefmt, arg...) \
> kthread_create_on_node(threadfn, data, -1, namefmt, ##arg)
>
> +#ifdef CONFIG_MODULE_KTHREAD_CHECK
> +unsigned long get_kthread_func(struct task_struct *tsk);
> +#else
> +#define get_kthread_func(tsk, addr, mod) (0)
> +#endif
This won't compile if CONFIG_MODULE_KTHREAD_CHECK=n.
Please make the stub function a proper C function, not a macro. It
provides type checking, can prevent compile warnings and is generally
easier on the eyes.
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1397,6 +1397,15 @@ config MODULE_FORCE_UNLOAD
> rmmod). This is mainly for kernel developers and desperate users.
> If unsure, say N.
>
> +config MODULE_KTHREAD_CHECK
> + bool "Check for runaway kernel threads at module unload"
> + depends on MODULE_UNLOAD && EXPERIMENTAL && DEBUG_KERNEL
> + help
> + This option allows you to check whether all kernel threads created
> + by the module and have used module code as a thread worker function
> + are really exited when the module is unloaded. This is mainly for
> + module developers. If insure, say N.
I think this should be under the kernel hacking menu, dependent on
CONFIG_DEBUG_KERNEL, in lib/Kconfig.debug.
> config MODVERSIONS
> bool "Module versioning support"
> help
> diff --git a/kernel/kthread.c b/kernel/kthread.c
> index 3d3de63..5c53817 100644
> --- a/kernel/kthread.c
> +++ b/kernel/kthread.c
> @@ -38,6 +38,9 @@ struct kthread_create_info
>
> struct kthread {
> int should_stop;
> +#ifdef CONFIG_MODULE_KTHREAD_CHECK
> + void *fn;
> +#endif
A little comment describing what this field is for would be nice.
> void *data;
> struct completion exited;
> };
> @@ -45,6 +48,24 @@ struct kthread {
> #define to_kthread(tsk) \
> container_of((tsk)->vfork_done, struct kthread, exited)
>
> +#ifdef CONFIG_MODULE_KTHREAD_CHECK
> +
> +unsigned long get_kthread_func(struct task_struct *tsk)
> +{
> + struct kthread *kt;
> + unsigned long addr;
> +
> + get_task_struct(tsk);
> + BUG_ON(!(tsk->flags & PF_KTHREAD));
> + kt = to_kthread(tsk);
> + barrier();
> + addr = tsk->vfork_done ? (unsigned long)kt->fn : 0UL;
> + put_task_struct(tsk);
> + return addr;
> +}
gack, I hadn't noticed the kthread ab^wre^wuse of vfork_done before.
Kooky. Undocumented, too.
> +#endif /* CONFIG_MODULE_KTHREAD_CHECK */
> +
> /**
> * kthread_should_stop - should this kthread return now?
> *
> @@ -106,6 +127,9 @@ static int kthread(void *_create)
> int ret;
>
> self.should_stop = 0;
> +#ifdef CONFIG_MODULE_KTHREAD_CHECK
> + self.fn = threadfn;
> +#endif
> self.data = data;
> init_completion(&self.exited);
> current->vfork_done = &self.exited;
> diff --git a/kernel/module.c b/kernel/module.c
> index 2c93276..fe6637b 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -45,6 +45,7 @@
> #include <linux/string.h>
> #include <linux/mutex.h>
> #include <linux/rculist.h>
> +#include <linux/kthread.h>
> #include <asm/uaccess.h>
> #include <asm/cacheflush.h>
> #include <asm/mmu_context.h>
> @@ -764,6 +765,49 @@ static void wait_for_zero_refcount(struct module *mod)
> mutex_lock(&module_mutex);
> }
>
> +#ifdef CONFIG_KALLSYMS
> +static const char *get_ksymbol(struct module *mod, unsigned long addr,
> + unsigned long *size, unsigned long *offset);
> +#else
> +#define get_ksymbol(mod, addr, size, offset) NULL
> +#endif
Can this code block be moved to after the get_ksymbol() definition so
the forward declaration is unneeded?
Did we really need to use the internal get_ksymbol(), rather than an
official kallsyms interface function?
The CONFIG_KALLSYMS=n stub should be written in C. Make it return
"<unknown>" and the ?: in check_kthreads() can be done away with.
> +#ifdef CONFIG_MODULE_KTHREAD_CHECK
> +
> +static void check_kthreads(struct module *mod)
> +{
> + unsigned long flags;
> + struct task_struct *g, *p;
> +
> + read_lock_irqsave(&tasklist_lock, flags);
> + do_each_thread(g, p) {
> + const char *name;
> + unsigned long addr, offset, size;
> +
> + /* Note kthreadd is special. Other kthreads should
> + have their 'struct kthread' on the stack until
> + do_exit() calls schedule() for the last time. */
> + if (p->mm || p == kthreadd_task)
> + continue;
> +
> + addr = get_kthread_func(p);
> + if (__module_text_address(addr) == mod) {
> + name = get_ksymbol(mod, addr, &size, &offset);
> + printk(KERN_WARNING "kthread %p[%s:%d] running "
> + "0x%lx(%s) is still alive, fix module %s, "
> + "crash possible\n", p, p->comm, p->pid, addr,
> + (name ? name : "<unknown>"), mod->name);
> + }
> + } while_each_thread(g, p);
> + read_unlock_irqrestore(&tasklist_lock, flags);
> +}
> +
> +#else
> +
> +#define check_kthreads(mod) do { } while (0)
In C, please.
> +#endif /* CONFIG_MODULE_KTHREAD_CHECK */
> +
> SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
> unsigned int, flags)
> {
> @@ -831,6 +875,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *,
> name_user,
> blocking_notifier_call_chain(&module_notify_list,
> MODULE_STATE_GOING, mod);
> async_synchronize_full();
> + check_kthreads(mod);
>
> /* Store the name of the last unloaded module for diagnostic purposes */
> strlcpy(last_unloaded_module, mod->name, sizeof(last_unloaded_module));
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