Adding Geert and timer people into Cc. On Thu 2018-05-31 17:08:49, Jia-Ju Bai wrote: > 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
The problem is in %pCr print format implementation. It calls clk_get_rate() that might sleep. I wonder if we could use some lock-less alternative instead. Anyway, we need to fix or remove this format. vsprintf-like functions are called in any context and nobody expect that they might sleep. In each case, printk() must call it under logbuf_lock spinlock. Otherwise, it would need to allocate a buffer for the formatted string and it is not acceptable. Best Regards, Petr > 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
