The patch titled
Subject: vfs,mm: fix a dead loop in truncate_inode_pages_range()
has been added to the -mm tree. Its filename is
vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range.patch
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------------------------------------------------------
From: Wei Fang <fangwei1@xxxxxxxxxx>
Subject: vfs,mm: fix a dead loop in truncate_inode_pages_range()
We triggered a deadloop in truncate_inode_pages_range() on 32 bits
architecture with the test case bellow:
...
fd = open();
write(fd, buf, 4096);
preadv64(fd, &iovec, 1, 0xffffffff000);
ftruncate(fd, 0);
...
Then ftruncate() will not return forever.
The filesystem used in this case is ubifs, but it can be triggered on many
other filesystems.
When preadv64() is called with offset=0xffffffff000, a page with
index=0xffffffff will be added to the radix tree of ->mapping. Then this
page can be found in ->mapping with pagevec_lookup(). After that,
truncate_inode_pages_range(), which is called in ftruncate(), will fall
into an infinite loop:
* find a page with index=0xffffffff, since index>=end, this page
won't be truncated
* index++, and index become 0
* the page with index=0xffffffff will be found again
The data type of index is unsigned long, so index won't overflow to 0 on
64 bits architecture in this case, and the dead loop won't happen.
Since truncate_inode_pages_range() is executed with holding lock of
inode->i_rwsem, any operation related with this lock will be blocked, and
a hung task will happen, e.g.:
INFO: task truncate_test:3364 blocked for more than 120 seconds.
...
[<c03c2c44>] call_rwsem_down_write_failed+0x17/0x30
[<c00b93bc>] generic_file_write_iter+0x32/0x1c0
[<c01b7078>] ubifs_write_iter+0xcc/0x170
[<c00fae48>] __vfs_write+0xc4/0x120
[<c00fb784>] vfs_write+0xb2/0x1b0
[<c00fbbe4>] SyS_write+0x46/0xa0
The page with index=0xffffffff added to ->mapping is useless. Fix this by
checking the read position before allocating pages.
Link: http://lkml.kernel.org/r/1475151010-40166-1-git-send-email-fangwei1@xxxxxxxxxx
Signed-off-by: Wei Fang <fangwei1@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 4 ++++
1 file changed, 4 insertions(+)
diff -puN mm/filemap.c~vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range mm/filemap.c
--- a/mm/filemap.c~vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range
+++ a/mm/filemap.c
@@ -1674,6 +1674,10 @@ static ssize_t do_generic_file_read(stru
unsigned int prev_offset;
int error = 0;
+ if (unlikely(*ppos >= inode->i_sb->s_maxbytes))
+ return -EINVAL;
+ iov_iter_truncate(iter, inode->i_sb->s_maxbytes);
+
index = *ppos >> PAGE_SHIFT;
prev_index = ra->prev_pos >> PAGE_SHIFT;
prev_offset = ra->prev_pos & (PAGE_SIZE-1);
_
Patches currently in -mm which might be from fangwei1@xxxxxxxxxx are
vfsmm-fix-a-dead-loop-in-truncate_inode_pages_range.patch
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