mm: xip/ext2 fix block allocation race (14bac5ac) · Commits · 戴 / test

XIP can call into get_xip_mem concurrently with the same file,offset with create=1. This usually maps down to get_block, which expects the page lock to prevent such a situation. This causes ext2 to explode for one reason or another. Serialise those calls for the moment. For common usages today, I suspect get_xip_mem rarely is called to create new blocks. In future as XIP technologies evolve we might need to look at which operations require scalability, and rework the locking to suit. Signed-off-by:

Nick Piggin <npiggin@suse.de> Cc: Jared Hulbert <jaredeh@gmail.com> Acked-by:

Carsten Otte <cotte@freenet.de> Cc: Hugh Dickins <hugh@veritas.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap_xip.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -248,15 +248,16 @@ again:
		int err;

		/* maybe shared writable, allocate new block */
		mutex_lock(&xip_sparse_mutex);
		error = mapping->a_ops->get_xip_mem(mapping, vmf->pgoff, 1,
		&xip_mem, &xip_pfn);
		mutex_unlock(&xip_sparse_mutex);
		if (error)
		return VM_FAULT_SIGBUS;
		/* unmap sparse mappings at pgoff from all other vmas */
		__xip_unmap(mapping, vmf->pgoff);

		found:
		printk("%s insert %lx@%lx\n", current->comm, (unsigned long)vmf->virtual_address, xip_pfn);
		err = vm_insert_mixed(vma, (unsigned long)vmf->virtual_address,
		xip_pfn);
		if (err == -ENOMEM)
		@@ -340,8 +341,10 @@ __xip_file_write(struct file filp, const char __user buf,
		&xip_mem, &xip_pfn);
		if (status == -ENODATA) {
		/* we allocate a new page unmap it */
		mutex_lock(&xip_sparse_mutex);
		status = a_ops->get_xip_mem(mapping, index, 1,
		&xip_mem, &xip_pfn);
		mutex_unlock(&xip_sparse_mutex);
		if (!status)
		/* unmap page at pgoff from all other vmas */
		__xip_unmap(mapping, index);

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