I am trying to mark a buffer for async write, but I am having a race condition
to unlock the buffer. I am doing.
bh = getbmapst(bdev, nsect); //this function calls bread
if (!bh) {
printk(KERN_ALERT "I/O error, bitmap cannot be trusted\n");
return -1;
}
lock_buffer(bh);
byte = bh->b_data + byteoffset;
*byte |= 1 << bitoffset;
lock_page(bh->b_page);
mark_page_accessed(bh->b_page);
__set_page_dirty_nobuffers(bh->b_page);
unlock_page(bh->b_page);
set_buffer_uptodate(bh);
mark_buffer_dirty(bh);
mark_buffer_async_write(bh);
unlock_buffer(bh);
brelse(bh);
What I want is the buffer head not to write synchronously when I do
the brelse, to
coalesce writes on it. It works normally, but this code has some form
of race condition.
The problem is that (in some circumstances, for example while using a
loop device against a file) this makes the fs/buffer.c:603
BUG_ON break. I am using the latest version of the kernel with SMP on a machine
with 4 processors.
Can anybody tell me what am I doing wrong?. I tried some other schemes, like
bit_spin_locking the BH_Uptodate_Lock, but they didn't work either.
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