Messages in this thread | | | Date | Mon, 10 Nov 2008 23:57:34 -0800 | From | Andrew Morton <> | Subject | Re: I2C from interrupt context? |
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On Fri, 07 Nov 2008 17:05:35 +0100 Krzysztof Halasa <khc@pm.waw.pl> wrote:
> Jean Delvare <khali@linux-fr.org> writes: > > > The situation is far from perfect though. For one thing, I seem to > > recall that Andrew Morton didn't like the approach taken in > > i2c_transfer(). For another, i2c_smbus_xfer() was not yet modified so > > at this point only I2C-level transactions can be non-sleeping, > > SMBus-level transactions can't. But all this could be fixed by anyone > > who cares about these specific issues. > > Thanks, I'll look at it.
The problem (well: bug) is that in_atomic() returns false inside a spinlock when CONFIG_PREEMPT=n. The code as it stands can sleep inside a spinlock, which is deadlockable if a scheduled-to task tries to take the same spinlock.
There is no means like this by which a piece of code can determine whether it can call schedule(). The pattern which we use in many many places (most especially GFP_KERNEL/GFP_ATOMIC) is to pass a flag down to callees telling them in some manner which context they were called from.
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