From: Aihua Zhang <zhangaihua1@xxxxxxxxxx>
I wrote a testcase to truncate a bin file while it is running on overlayfs.
the mount:
/dev/mapper/fedora-home on /home type ext4 (rw,relatime,data=ordered)
overlay on /tmp type overlay (rw,relatime,lowerdir=/home/zah/lower,
upperdir=/home/zah/upper,workdir=/home/zah/workdir)
the code cpp:
int main(int argc, char *argv[])
{
int status;
pthread_t thread;
int err;
char *ptr;
ptr = basename(argv[0]);
printf("%s\n",ptr);
errno = 0;
status = truncate(ptr, 4096);
printf("status:%d\n",status);
printf("errno:%d\n",errno);
printf("ETXTBSY:%d\n",ETXTBSY);
if ((-1 == status) && (ETXTBSY == errno))
{
printf("PASS\n");
return 0;
}
err = errno;
printf("err = %d\n", err);
printf("FAIL\n");
return 1;
}
I running the test on overlayfs, the result as below:
Bus error (core dumped)
and running the test on ext4, the result as below:
status:-1
errno:26
ETXTBSY:26
PASS
I add some log, and I find the inode is not correct on overlayfs,
and the inode->i_writecount is not correct also called by vfs_truncate->
get_write_access(), the log as below:
Jun 22 09:50:38 kernel: [131.872920] deny_write_access: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873109] deny_write_access: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873110] __vma_link_file: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873112] allow_write_access: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873114] deny_write_access: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873115] __vma_link_file: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873116] allow_write_access: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873162] allow_write_access: inode ino 64104618
Jun 22 09:50:38 kernel: [131.873947] __vma_link_file: inode ino 64104618
Jun 22 09:50:38 kernel: [131.874039] vfs_truncate: inode ino:24061
before vfs_truncate, the inode is point to upper filesystem(ext4),
and in vfs_truncate the inode is point to overlayfs.
So, I fix it by geting the real inode via ovl_d_select_inode.
Signed-off-by: Aihua Zhang <zhangaihua1@xxxxxxxxxx>
---
fs/open.c | 10 ++++++++--
1 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/fs/open.c b/fs/open.c
index 93ae3cd..43b17d1 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -67,10 +67,16 @@ int do_truncate(struct dentry *dentry, loff_t length, unsigned int time_attrs,
long vfs_truncate(const struct path *path, loff_t length)
{
+ struct dentry *dentry = path->dentry;
struct inode *inode;
long error;
- inode = path->dentry->d_inode;
+ if (dentry->d_flags & DCACHE_OP_SELECT_INODE) {
+ inode = dentry->d_op->d_select_inode(dentry, O_TRUNC);
+ if (IS_ERR(inode))
+ return PTR_ERR(inode);
+ } else
+ inode = dentry->d_inode;
/* For directories it's -EISDIR, for other non-regulars - -EINVAL */
if (S_ISDIR(inode->i_mode))
@@ -106,7 +112,7 @@ long vfs_truncate(const struct path *path, loff_t length)
if (!error)
error = security_path_truncate(path);
if (!error)
- error = do_truncate(path->dentry, length, 0, NULL);
+ error = do_truncate(dentry, length, 0, NULL);
put_write_and_out:
put_write_access(inode);
--
1.7.1
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