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Commit 5ffd3412 authored by Thomas Betker's avatar Thomas Betker Committed by Artem Bityutskiy
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jffs2: Fix lock acquisition order bug in jffs2_write_begin 



jffs2_write_begin() first acquires the page lock, then f->sem. This
causes an AB-BA deadlock with jffs2_garbage_collect_live(), which first
acquires f->sem, then the page lock:

jffs2_garbage_collect_live
    mutex_lock(&f->sem)                         (A)
    jffs2_garbage_collect_dnode
        jffs2_gc_fetch_page
            read_cache_page_async
                do_read_cache_page
                    lock_page(page)             (B)

jffs2_write_begin
    grab_cache_page_write_begin
        find_lock_page
            lock_page(page)                     (B)
    mutex_lock(&f->sem)                         (A)

We fix this by restructuring jffs2_write_begin() to take f->sem before
the page lock. However, we make sure that f->sem is not held when
calling jffs2_reserve_space(), as this is not permitted by the locking
rules.

The deadlock above was observed multiple times on an SoC with a dual
ARMv7 (Cortex-A9), running the long-term 3.4.11 kernel; it occurred
when using scp to copy files from a host system to the ARM target
system. The fix was heavily tested on the same target system.

Cc: stable@vger.kernel.org
Signed-off-by: default avatarThomas Betker <thomas.betker@rohde-schwarz.com>
Acked-by: default avatarJoakim Tjernlund <Joakim.Tjernlund@transmode.se>
Signed-off-by: default avatarArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
parent 0131950e

fs/jffs2/file.c

+21 −18
Original line number Diff line number Diff line
@@ -138,33 +138,39 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, 
	struct page *pg;

	struct inode *inode = mapping->host;

	struct jffs2_inode_info *f = JFFS2_INODE_INFO(inode);

	struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);

	struct jffs2_raw_inode ri;

	uint32_t alloc_len = 0;

	pgoff_t index = pos >> PAGE_CACHE_SHIFT;

	uint32_t pageofs = index << PAGE_CACHE_SHIFT;

	int ret = 0;



	jffs2_dbg(1, "%s()\n", __func__);



	if (pageofs > inode->i_size) {

		ret = jffs2_reserve_space(c, sizeof(ri), &alloc_len,

					  ALLOC_NORMAL, JFFS2_SUMMARY_INODE_SIZE);

		if (ret)

			return ret;

	}



	mutex_lock(&f->sem);

	pg = grab_cache_page_write_begin(mapping, index, flags);

	if (!pg)

	if (!pg) {

		if (alloc_len)

			jffs2_complete_reservation(c);

		mutex_unlock(&f->sem);

		return -ENOMEM;

	}

	*pagep = pg;



	jffs2_dbg(1, "%s()\n", __func__);



	if (pageofs > inode->i_size) {

	if (alloc_len) {

		/* Make new hole frag from old EOF to new page */

		struct jffs2_sb_info *c = JFFS2_SB_INFO(inode->i_sb);

		struct jffs2_raw_inode ri;

		struct jffs2_full_dnode *fn;

		uint32_t alloc_len;



		jffs2_dbg(1, "Writing new hole frag 0x%x-0x%x between current EOF and new page\n",

			  (unsigned int)inode->i_size, pageofs);



		ret = jffs2_reserve_space(c, sizeof(ri), &alloc_len,

					  ALLOC_NORMAL, JFFS2_SUMMARY_INODE_SIZE);

		if (ret)

			goto out_page;



		mutex_lock(&f->sem);

		memset(&ri, 0, sizeof(ri));



		ri.magic = cpu_to_je16(JFFS2_MAGIC_BITMASK);
@@ -191,7 +197,6 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, 
		if (IS_ERR(fn)) {

			ret = PTR_ERR(fn);

			jffs2_complete_reservation(c);

			mutex_unlock(&f->sem);

			goto out_page;

		}

		ret = jffs2_add_full_dnode_to_inode(c, f, fn);
@@ -206,12 +211,10 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, 
			jffs2_mark_node_obsolete(c, fn->raw);

			jffs2_free_full_dnode(fn);

			jffs2_complete_reservation(c);

			mutex_unlock(&f->sem);

			goto out_page;

		}

		jffs2_complete_reservation(c);

		inode->i_size = pageofs;

		mutex_unlock(&f->sem);

	}



	/*
@@ -220,18 +223,18 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, 
	 * case of a short-copy.

	 */

	if (!PageUptodate(pg)) {

		mutex_lock(&f->sem);

		ret = jffs2_do_readpage_nolock(inode, pg);

		mutex_unlock(&f->sem);

		if (ret)

			goto out_page;

	}

	mutex_unlock(&f->sem);

	jffs2_dbg(1, "end write_begin(). pg->flags %lx\n", pg->flags);

	return ret;



out_page:

	unlock_page(pg);

	page_cache_release(pg);

	mutex_unlock(&f->sem);

	return ret;

}