linux-kernel - Re: USB device cannot be reconnected and khubd "blocked for more than 120 seconds"

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Date:	Tue, 15 Jan 2013 14:23:47 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alex Riesen <raa.lkml@...il.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Jens Axboe <axboe@...nel.dk>,
	USB list <linux-usb@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: USB device cannot be reconnected and khubd "blocked for more than
 120 seconds"

On Tue, Jan 15, 2013 at 9:53 AM, Ming Lei <ming.lei@...onical.com> wrote:
>
> I will try to figure out one patch to address the scsi block async probe
> issue first, and see if it can fix the problem by moving add_disk()
> into sd_probe()
> and calling async_synchronize_full_domain(&scsi_sd_probe_domain)
> in the entry of sd_open().

Looks it isn't doable because the block partition device can only be created
inside the async things.

But I have another idea to address the problem, and let module code call
async_synchronize_full() only if the module requires that explicitly, so how
about the below draft patch?

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 7992635..c5106a0 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3143,6 +3143,8 @@ static int __init init_sd(void)
 	if (err)
 		goto err_out_driver;

+	mod_init_async_wait(THIS_MODULE);
+
 	return 0;

 err_out_driver:
diff --git a/include/linux/module.h b/include/linux/module.h
index 7760c6d..09bd4c5 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -300,6 +300,12 @@ struct module

 	unsigned int taints;	/* same bits as kernel:tainted */

+	/*
+	 * set if the module wants to call async_synchronize_full
+	 * after its init() is complted.
+	 */
+	unsigned int init_async_wait:1;
+
 #ifdef CONFIG_GENERIC_BUG
 	/* Support for BUG */
 	unsigned num_bugs;
@@ -656,4 +662,16 @@ static inline void module_bug_finalize(const Elf_Ehdr *hdr,
 static inline void module_bug_cleanup(struct module *mod) {}
 #endif	/* CONFIG_GENERIC_BUG */

+/*
+ * If one module wants to complete its all async code after
+ * its init() executed, the module can call this function in
+ * the entry of its init(), but the module's async function
+ * can't call request_module, otherwise deadlock will be caused.
+ */
+static inline void mod_init_async_wait(struct module *mod)
+{
+	if (mod)
+		mod->init_async_wait = 1;
+}
+
 #endif /* _LINUX_MODULE_H */
diff --git a/kernel/module.c b/kernel/module.c
index 250092c..dc5d011 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3058,8 +3058,9 @@ static int do_init_module(struct module *mod)
 	blocking_notifier_call_chain(&module_notify_list,
 				     MODULE_STATE_LIVE, mod);

-	/* We need to finish all async code before the module init sequence is done */
-	async_synchronize_full();
+	/* Only complete all async code if the module requires that */
+	if (mod->init_async_wait)
+		async_synchronize_full();

 	mutex_lock(&module_mutex);
 	/* Drop initial reference. */


Thanks,
--
Ming Lei
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