Hi. I have a function that enters with a lock held and does
an unlock inside a loop.
Sparse 0.4.4 is fine with this function until I introduce a conditional
between the unlock and the next lock. In the minimal example below,
changing the "#if 1" to "#if 0" makes sparse generate the warning
below:
cd ~/git/linux && PATH=/opt/bin:$PATH make drivers/block/aoe/aoe.ko C=1
make[1]: Nothing to be done for `all'.
make[1]: Nothing to be done for `relocs'.
CHK include/linux/version.h
CHK include/generated/utsrelease.h
CALL scripts/checksyscalls.sh
CHECK drivers/block/aoe/demo.c
/build/ecashin/git/linux/arch/x86/include/asm/spinlock.h:81:9: warning: context imbalance in 'demofn' - unexpected unlock
CC [M] drivers/block/aoe/demo.o
LD [M] drivers/block/aoe/aoe.o
MODPOST 1 modules
CC drivers/block/aoe/aoe.mod.o
LD [M] drivers/block/aoe/aoe.ko
I'm using 3.6.0-rc7 kernel sources.
Granted, I'm unusually tired today, but I can't think of a way that
conditionally printing a warning has changed the locking, so I
could use some help in determining whether this is a sparse bug
that might be fixed, one that I have to work around, or some
confusion of mine.
/* demo.c */
#include <linux/netdevice.h>
static spinlock_t lk;
static struct sk_buff_head q;
int demofn(void);
/* enters and returns with lk held */
int demofn(void)
{
struct sk_buff *skb;
while ((skb = skb_dequeue(&q))) {
spin_unlock_irq(&lk);
#if 1
dev_queue_xmit(skb);
#else
if (dev_queue_xmit(skb) == NET_XMIT_DROP && net_ratelimit())
pr_warn("informative warning\n");
#endif
spin_lock_irq(&lk);
}
return 0;
}
--
Ed Cashin
ecashin@xxxxxxxxxx http://www.coraid.com/
ecashin@xxxxxxxxxxxx http://noserose.net/e/
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