JFFS2 oops when writing to two partitions simultaneously

[Joakim Tjernlund]

linux-mtd-bounces at lists.infradead.org wrote on 2012/01/26 10:02:07:

> From: Orjan Friberg <of at flatfrog.com>
> To: <linux-mtd at lists.infradead.org>
> Date: 2012/01/26 10:15
> Subject: Re: JFFS2 oops when writing to two partitions simultaneously
> Sent by: linux-mtd-bounces at lists.infradead.org
>
> On 01/25/2012 10:01 PM, Orjan Friberg wrote:
> > That one-liner was boiled down from the following program, which still
> > oopses instantly:
>
> The C program seems to work fine with CONFIG_PREEMPT_NONE=y.
>
> If that is indeed the problem I guess it's reasonable that it worked
> better with PREEMPT_VOLUNTARY than PREEMPT because there are fewer
> preemtion points.

The spin locking in jffs2_compress() seems broken:

	case JFFS2_COMPR_MODE_SIZE:
	case JFFS2_COMPR_MODE_FAVOURLZO:
		orig_slen = *datalen;
		orig_dlen = *cdatalen;
		spin_lock(&jffs2_compressor_list_lock);
		list_for_each_entry(this, &jffs2_compressor_list, list) {
			/* Skip decompress-only backwards-compatibility and disabled modules */
			if ((!this->compress)||(this->disabled))
				continue;
			/* Allocating memory for output buffer if necessary */
			if ((this->compr_buf_size < orig_slen) && (this->compr_buf)) {
				spin_unlock(&jffs2_compressor_list_lock);

				kfree(this->compr_buf);
				spin_lock(&jffs2_compressor_list_lock);
				this->compr_buf_size=0;
				this->compr_buf=NULL;
			}

....

if 2 threads are competing here, I don't think you can drop the spin lock
temporarily as this routine do.

 Jocke