This is a note to let you know that I've just added the patch titled jffs2: GC deadlock reading a page that is used in jffs2_write_begin() to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: jffs2-gc-deadlock-reading-a-page-that-is-used-in-jff.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 43f86f9bd4a9c3bc2450579a6dd2e8ff61611b24 Author: Kyeong Yoo <kyeong.yoo@xxxxxxxxxxxxxxxxxxx> Date: Tue Jul 4 16:22:38 2017 +1200 jffs2: GC deadlock reading a page that is used in jffs2_write_begin() [ Upstream commit aa39cc675799bc92da153af9a13d6f969c348e82 ] GC task can deadlock in read_cache_page() because it may attempt to release a page that is actually allocated by another task in jffs2_write_begin(). The reason is that in jffs2_write_begin() there is a small window a cache page is allocated for use but not set Uptodate yet. This ends up with a deadlock between two tasks: 1) A task (e.g. file copy) - jffs2_write_begin() locks a cache page - jffs2_write_end() tries to lock "alloc_sem" from jffs2_reserve_space() <-- STUCK 2) GC task (jffs2_gcd_mtd3) - jffs2_garbage_collect_pass() locks "alloc_sem" - try to lock the same cache page in read_cache_page() <-- STUCK So to avoid this deadlock, hold "alloc_sem" in jffs2_write_begin() while reading data in a cache page. Signed-off-by: Kyeong Yoo <kyeong.yoo@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Richard Weinberger <richard@xxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c index 4fc8cd698d1a4..bd7d58d27bfc6 100644 --- a/fs/jffs2/file.c +++ b/fs/jffs2/file.c @@ -136,20 +136,15 @@ 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); pgoff_t index = pos >> PAGE_SHIFT; uint32_t pageofs = index << PAGE_SHIFT; int ret = 0; - pg = grab_cache_page_write_begin(mapping, index, flags); - if (!pg) - return -ENOMEM; - *pagep = pg; - jffs2_dbg(1, "%s()\n", __func__); if (pageofs > inode->i_size) { /* 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; @@ -160,7 +155,7 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, ret = jffs2_reserve_space(c, sizeof(ri), &alloc_len, ALLOC_NORMAL, JFFS2_SUMMARY_INODE_SIZE); if (ret) - goto out_page; + goto out_err; mutex_lock(&f->sem); memset(&ri, 0, sizeof(ri)); @@ -190,7 +185,7 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, ret = PTR_ERR(fn); jffs2_complete_reservation(c); mutex_unlock(&f->sem); - goto out_page; + goto out_err; } ret = jffs2_add_full_dnode_to_inode(c, f, fn); if (f->metadata) { @@ -205,13 +200,26 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, jffs2_free_full_dnode(fn); jffs2_complete_reservation(c); mutex_unlock(&f->sem); - goto out_page; + goto out_err; } jffs2_complete_reservation(c); inode->i_size = pageofs; mutex_unlock(&f->sem); } + /* + * While getting a page and reading data in, lock c->alloc_sem until + * the page is Uptodate. Otherwise GC task may attempt to read the same + * page in read_cache_page(), which causes a deadlock. + */ + mutex_lock(&c->alloc_sem); + pg = grab_cache_page_write_begin(mapping, index, flags); + if (!pg) { + ret = -ENOMEM; + goto release_sem; + } + *pagep = pg; + /* * Read in the page if it wasn't already present. Cannot optimize away * the whole page write case until jffs2_write_end can handle the @@ -221,15 +229,17 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping, mutex_lock(&f->sem); ret = jffs2_do_readpage_nolock(inode, pg); mutex_unlock(&f->sem); - if (ret) - goto out_page; + if (ret) { + unlock_page(pg); + put_page(pg); + goto release_sem; + } } jffs2_dbg(1, "end write_begin(). pg->flags %lx\n", pg->flags); - return ret; -out_page: - unlock_page(pg); - put_page(pg); +release_sem: + mutex_unlock(&c->alloc_sem); +out_err: return ret; }