On Fri, 16 Apr 2010 11:58:19 +0100
That debug check got inadvertently crippled during some wait_on_bit()
conversion.
It's still a nasty bug to call wait_on_buffer() against a zero-ref
buffer so perhaps we should fix it up rather than removing its remains.
diff -puN include/linux/buffer_head.h~buffer_head-remove-redundant-test-from-wait_on_buffer-fix include/linux/buffer_head.h
--- a/include/linux/buffer_head.h~buffer_head-remove-redundant-test-from-wait_on_buffer-fix
+++ a/include/linux/buffer_head.h
@@ -305,10 +305,15 @@ map_bh(struct buffer_head *bh, struct su
bh->b_size = sb->s_blocksize;
}
+/*
+ * Calling wait_on_buffer() for a zero-ref buffer is illegal, so we call into
+ * __wait_on_buffer() just to trip a debug check. Because debug code in inline
+ * functions is bloaty.
+ */
static inline void wait_on_buffer(struct buffer_head *bh)
{
might_sleep();
- if (buffer_locked(bh))
+ if (buffer_locked(bh) || atomic_read(&bh->b_count) == 0)
__wait_on_buffer(bh);
}
diff -puN fs/buffer.c~buffer_head-remove-redundant-test-from-wait_on_buffer-fix fs/buffer.c
--- a/fs/buffer.c~buffer_head-remove-redundant-test-from-wait_on_buffer-fix
+++ a/fs/buffer.c
@@ -90,6 +90,12 @@ EXPORT_SYMBOL(unlock_buffer);
*/
void __wait_on_buffer(struct buffer_head * bh)
{
+ /*
+ * Calling wait_on_buffer() against a zero-ref buffer is a nasty bug
+ * because it will almost always "work". However this buffer can be
+ * reclaimed at any time. So check for it.
+ */
+ VM_BUG_ON(atomic_read(&bh->b_count) == 0);
wait_on_bit(&bh->b_state, BH_Lock, sync_buffer, TASK_UNINTERRUPTIBLE);
}
EXPORT_SYMBOL(__wait_on_buffer);
_
And while we're there...
This might make reiserfs explode.
From: Andrew Morton <akpm@linux-foundation.org>
The first thing __wait_on_buffer()->wait_on_bit() does is to test that the
bit was set, so the buffer_locked() test is now redundant. And once we
remove that, we can remove the check for zero ->b_count also.
And now that ...
