linux-kernel - Kernel boot hangs on commit "switch fput to task_work

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Date:	Tue, 10 Jul 2012 22:18:30 +0800
From:	wfg@...ux.intel.com
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Kernel boot hangs on commit "switch fput to task_work_add"

Hi Al,

The linux-next kernel reliably hung after this line:

[    4.846260] debug: unmapping init [mem 0xffff88000182a000-0xffff8800019fffff]

And it's bisected to commit:

        commit 4a9ffe81385c2af04f296bea05482f34e02ea10d
        Author: Al Viro <viro@...iv.linux.org.uk>
        Date:   Sun Jun 24 09:56:45 2012 +0400

            switch fput to task_work_add

            ... and schedule_work() for interrupt/kernel_thread callers
            (and yes, now it *is* OK to call from interrupt).

I tried add this debug aid:

init_post(void):
+       printk(KERN_WARNING "flush_delayed_fput\n");
        flush_delayed_fput();
+       printk(KERN_WARNING "flush_delayed_fput done\n");

And then it hangs after "flush_delayed_fput done". So it's not directly
freezing inside flush_delayed_fput()..

Thanks,
Fengguang

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