Re: use of preempt_count instead of in_atomic() at leds-gpio.c
From: Andrew Morton
Date: Thu Mar 20 2008 - 21:10:46 EST
On Thu, 20 Mar 2008 21:36:04 -0300 Henrique de Moraes Holschuh <hmh@xxxxxxxxxx> wrote:
> Well, so far so good for LEDs, but what about the other users of in_atomic
> that apparently should not be doing it either?
Ho hum. Lots of cc's added.
./arch/x86/mm/pageattr.c
Looks wrong.
./arch/m68k/atari/time.c
Possibly buggy: deadlockable
./sound/core/seq/seq_virmidi.c
Possibly buggy
./net/iucv/iucv.c
./kernel/power/process.c
Just a debug check.
./drivers/s390/char/sclp_tty.c
Possibly buggy: deadlockable
./drivers/s390/char/sclp_vt220.c
Possibly buggy: deadlockable
./drivers/s390/net/netiucv.c
Possibly buggy: deadlockable
./drivers/char/isicom.c
Possibly buggy: deadlockable
./drivers/usb/misc/sisusbvga/sisusb_con.c
Possibly buggy: deadlockable
./drivers/net/usb/pegasus.c
Possibly buggy: deadlockable (I assume)
./drivers/net/wireless/airo.c
Possibly buggy: deadlockable
./drivers/net/wireless/rt2x00/rt73usb.c
Possibly buggy: deadlockable (I assume)
./drivers/net/wireless/rt2x00/rt2500usb.c
Possibly buggy: deadlockable (I assume)
./drivers/net/wireless/hostap/hostap_ioctl.c
Possibly buggy: deadlockable (I assume)
./drivers/net/wireless/zd1211rw/zd_usb.c
Possibly buggy: deadlockable (I assume)
./drivers/net/irda/sir_dev.c
Possibly buggy: deadlockable
./drivers/net/netxen/netxen_nic_niu.c
Possibly buggy: deadlockable
./drivers/net/netxen/netxen_nic_init.c
Possibly buggy: deadlockable
./drivers/ieee1394/ieee1394_transactions.c
Possibly buggy: deadlockable
./drivers/video/amba-clcd.c
Possibly buggy: deadlockable
./drivers/i2c/i2c-core.c
Possibly buggy: deadlockable
The usual pattern for most of the above is
if (!in_atomic())
do_something_which_might_sleep();
problem is, in_atomic() returns false inside spinlock on non-preptible
kernels. So if anyone calls those functions inside spinlock they will
incorrectly schedule and another task can then come in and try take the
already-held lock.
Now, it happens that in_atomic() returns true on non-preemtible kernels
when running in interrupt or softirq context. But if the above code really
is using in_atomic() to detect am-i-called-from-interrupt and NOT
am-i-called-from-inside-spinlock, they should be using in_irq(),
in_softirq() or in_interrupt().
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