linux-kernel - Can printk() sleep at runtime?

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Date:   Thu, 31 May 2018 17:08:49 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     bhelgaas@...gle.com, pmladek@...e.com,
        sergey.senozhatsky@...il.com, rostedt@...dmis.org,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg KH <gregkh@...uxfoundation.org>, corbet@....net,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Can printk() sleep at runtime?

Hello,

I write a static analysis tool (DSAC), and it finds that printk can sleep.
According to this finding, there is an example bug in drivers/pci/pci.c 
in Linux-4.16.7.

Here is the call path for this bug.
Please look at it *from the bottom up*.

========== BUG ==========
[FUNC] __might_sleep
kernel/locking/mutex.c: 747: __might_sleep in __mutex_lock_common
kernel/locking/mutex.c: 893: __mutex_lock_common in __mutex_lock
kernel/locking/mutex.c: 908: __mutex_lock in mutex_lock_nested
drivers/clk/clk.c, 123: mutex_lock_nested in clk_prepare_lock
drivers/clk/clk.c, 1369: clk_prepare_lock in clk_core_get_rate
drivers/clk/clk.c, 1393: clk_core_get_rate in clk_get_rate
lib/vsprintf.c, 1450: clk_get_rate in clock
lib/vsprintf.c, 1944: clock in pointer
lib/vsprintf.c, 2286: pointer in vsnprintf
lib/vsprintf.c, 2385: vsnprintf in vscnprintf
kernel/printk/printk.c, 1853: vscnprintf in vprintk_emit
kernel/printk/printk.c, 1947: vprintk_emit in vprintk_default
kernel/printk/printk_safe.c, 379: vprintk_default in vprintk_func
kernel/printk/printk.c, 1980: vprintk_func in printk
drivers/pci/pci.c, 5364: printk in pci_specified_resource_alignment
drivers/pci/pci.c, 5313: spin_lock in pci_specified_resource_alignment

In fact, I suspect that my report is false, because I always have an 
impression that printk() cannot sleep.
But according to the call path, I cannot find where I make the mistake...

So could someone please help me to point the mistake?


Best wishes,
Jia-Ju Bai