From: yangerkun yangerkun@huawei.com
commit 565333a1554d704789e74205989305c811fd9c7a upstream.
No need to wait for any commit once the page is fully truncated. Besides, it may confuse e.g. concurrent ext4_writepage() with the page still be dirty (will be cleared by truncate_pagecache() in ext4_setattr()) but buffers has been freed; and then trigger a bug show as below:
[ 26.057508] ------------[ cut here ]------------ [ 26.058531] kernel BUG at fs/ext4/inode.c:2134! ... [ 26.088130] Call trace: [ 26.088695] ext4_writepage+0x914/0xb28 [ 26.089541] writeout.isra.4+0x1b4/0x2b8 [ 26.090409] move_to_new_page+0x3b0/0x568 [ 26.091338] __unmap_and_move+0x648/0x988 [ 26.092241] unmap_and_move+0x48c/0xbb8 [ 26.093096] migrate_pages+0x220/0xb28 [ 26.093945] kernel_mbind+0x828/0xa18 [ 26.094791] __arm64_sys_mbind+0xc8/0x138 [ 26.095716] el0_svc_common+0x190/0x490 [ 26.096571] el0_svc_handler+0x60/0xd0 [ 26.097423] el0_svc+0x8/0xc
Run the procedure (generate by syzkaller) parallel with ext3.
void main() { int fd, fd1, ret; void *addr; size_t length = 4096; int flags; off_t offset = 0; char *str = "12345";
fd = open("a", O_RDWR | O_CREAT); assert(fd >= 0);
/* Truncate to 4k */ ret = ftruncate(fd, length); assert(ret == 0);
/* Journal data mode */ flags = 0xc00f; ret = ioctl(fd, _IOW('f', 2, long), &flags); assert(ret == 0);
/* Truncate to 0 */ fd1 = open("a", O_TRUNC | O_NOATIME); assert(fd1 >= 0);
addr = mmap(NULL, length, PROT_WRITE | PROT_READ, MAP_SHARED, fd, offset); assert(addr != (void *)-1);
memcpy(addr, str, 5); mbind(addr, length, 0, 0, 0, MPOL_MF_MOVE); }
And the bug will be triggered once we seen the below order.
reproduce1 reproduce2
... | ... truncate to 4k | change to journal data mode | | memcpy(set page dirty) truncate to 0: | ext4_setattr: | ... | ext4_wait_for_tail_page_commit | | mbind(trigger bug) truncate_pagecache(clean dirty)| ... ... |
mbind will call ext4_writepage() since the page still be dirty, and then report the bug since the buffers has been free. Fix it by return directly once offset equals to 0 which means the page has been fully truncated.
Reported-by: Hulk Robot hulkci@huawei.com Signed-off-by: yangerkun yangerkun@huawei.com Link: https://lore.kernel.org/r/20190919063508.1045-1-yangerkun@huawei.com Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Theodore Ts'o tytso@mit.edu Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/inode.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
--- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -5305,11 +5305,15 @@ static void ext4_wait_for_tail_page_comm
offset = inode->i_size & (PAGE_SIZE - 1); /* - * All buffers in the last page remain valid? Then there's nothing to - * do. We do the check mainly to optimize the common PAGE_SIZE == - * blocksize case + * If the page is fully truncated, we don't need to wait for any commit + * (and we even should not as __ext4_journalled_invalidatepage() may + * strip all buffers from the page but keep the page dirty which can then + * confuse e.g. concurrent ext4_writepage() seeing dirty page without + * buffers). Also we don't need to wait for any commit if all buffers in + * the page remain valid. This is most beneficial for the common case of + * blocksize == PAGESIZE. */ - if (offset > PAGE_SIZE - i_blocksize(inode)) + if (!offset || offset > (PAGE_SIZE - i_blocksize(inode))) return; while (1) { page = find_lock_page(inode->i_mapping,