Messages in this thread | | | Date | Tue, 4 Jun 2013 09:37:49 -0400 | From | Theodore Ts'o <> | Subject | Re: [PATCH 1/2] jbd2: check bh->b_data for NULL in jbd2_journal_get_descriptor_buffer before memset() |
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On Tue, Jun 04, 2013 at 02:15:57PM +0300, Ruslan Bilovol wrote: > > Have you actually seen a case where bh is non-NULL, but bh->b_data is > > NULL? If not, it might be better to do something like this: > > Yes, this is exactly the situation I observe (bh is non-NULL, but > bh->b_data is NULL)
Hmm... so the stack trace you sent in the commit description was one where bh->b_data was NULL? I'm trying to make sure there isn't something else going on that we don't understand.
Could you put some instrumentation in __find_get_block()? Something like this:
struct buffer_head * __find_get_block(struct block_device *bdev, sector_t block, unsigned size) { struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
if (bh == NULL) { bh = __find_get_block_slow(bdev, block); if (bh->b_data == NULL) { pr_crit("b_data NULL after find_get_block_slow\n); WARN_ON(1); } if (bh) bh_lru_install(bh); } else { if (bh->b_data == NULL) { pr_crit("b_data NULL after lookup_bh_lru\n"); WARN_ON(1); } } if (bh) touch_buffer(bh); return bh; }
... and then send me the stack trace after running your reproduction case. If it turns out the problem is in __find_get_block_slow(), could you put in similar debugging checks there and try to track it down?
I'm pretty sure the case of bh non-NULL and bh->b_data NULL is never supposed to happen, and while we could just put a check where you suggested, there are plenty of other places which use __getblk(), and there may be other bugs that are hiding here.
Regards,
- Ted
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