Hello,
I am back porting an RT patch from 2.6.33 version to 2.6.32 version and
this question
is in that context. Thanks in advance for you reply!
cond_resched_lock() calls __might_sleep with PREEMPT_LOCK_OFFSET as 1.
And when
preempt count is equal to 0 it would print the warning like below.
Warning
--------
BUG: sleeping function called from invalid context at fs/jbd/commit.c:902
pcnt: 0 1 in_atomic(): 0, irqs_disabled(): 0, pid: 818, name: kjournald
Q1. Why is it ok for preempt_count to be 1 when irqs are disabled but not
when preempt_count is 1?
I am getting the warning above when
cond_resched_lock(&journal->j_list_lock) is invoked from
journal_commit_transaction(journal_t *journal) in fs/jbd/commit.c:902
cond_resched_lock code
----------------------
#ifdef CONFIG_PREEMPT
#define PREEMPT_LOCK_OFFSET PREEMPT_OFFSET
#else
#define PREEMPT_LOCK_OFFSET 0
#endif
#define cond_resched_lock(lock) ({ \
__might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET); \
__cond_resched_lock(lock); \
})
__might_sleep code
--------------------
void __might_sleep(char *file, int line, int preempt_offset)
{
#ifdef in_atomic
static unsigned long prev_jiffy; /* ratelimiting */
if ((preempt_count_equals(preempt_offset) && !irqs_disabled()) ||
system_state != SYSTEM_RUNNING || oops_in_progress)
return;
if (time_before(jiffies, prev_jiffy + HZ) && prev_jiffy)
return;
prev_jiffy = jiffies;
printk(KERN_ERR
"BUG: sleeping function called from invalid context at %s:%d\n",
.......
.......
}
preempt_count_equals() code
----------------------------
#if defined(CONFIG_DEBUG_SPINLOCK_SLEEP) || defined(CONFIG_DEBUG_PREEMPT)
static inline int preempt_count_equals(int preempt_offset)
{
int nested = (preempt_count() & ~PREEMPT_ACTIVE);
#ifndef CONFIG_PREEMPT_RT
nested += rcu_preempt_depth();
#endif
return (nested == preempt_offset);
}
-Venkat
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