nfsd/ksmbd call vfs_copy_file_range() with flag COPY_FILE_SPLICE to
perform kernel copy between two files on any two filesystems.
Splicing input file, while holding file_start_write() on the output file
which is on a different sb, posses a risk for fanotify related deadlocks.
We only need to call splice_file_range() from within the context of
->copy_file_range() filesystem methods with file_start_write() held.
To avoid the possible deadlocks, always use do_splice_direct() instead of
splice_file_range() for the kernel copy fallback in vfs_copy_file_range()
without holding file_start_write().
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
fs/read_write.c | 36 +++++++++++++++++++++++-------------
1 file changed, 23 insertions(+), 13 deletions(-)
diff --git a/fs/read_write.c b/fs/read_write.c
index 0bc99f38e623..e0c2c1b5962b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1421,6 +1421,10 @@ ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
size_t len, unsigned int flags)
{
+ /* May only be called from within ->copy_file_range() methods */
+ if (WARN_ON_ONCE(flags))
+ return -EINVAL;
+
return splice_file_range(file_in, &pos_in, file_out, &pos_out,
min_t(size_t, len, MAX_RW_COUNT));
}
@@ -1541,19 +1545,22 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
ret = file_out->f_op->copy_file_range(file_in, pos_in,
file_out, pos_out,
len, flags);
- goto done;
- }
-
- if (!splice && file_in->f_op->remap_file_range &&
- file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
+ } else if (!splice && file_in->f_op->remap_file_range &&
+ file_inode(file_in)->i_sb == file_inode(file_out)->i_sb) {
ret = file_in->f_op->remap_file_range(file_in, pos_in,
file_out, pos_out,
min_t(loff_t, MAX_RW_COUNT, len),
REMAP_FILE_CAN_SHORTEN);
- if (ret > 0)
- goto done;
+ /* fallback to splice */
+ if (ret <= 0)
+ splice = true;
}
+ file_end_write(file_out);
+
+ if (!splice)
+ goto done;
+
/*
* We can get here for same sb copy of filesystems that do not implement
* ->copy_file_range() in case filesystem does not support clone or in
@@ -1565,11 +1572,16 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
* and which filesystems do not, that will allow userspace tools to
* make consistent desicions w.r.t using copy_file_range().
*
- * We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE.
+ * We also get here if caller (e.g. nfsd) requested COPY_FILE_SPLICE
+ * for server-side-copy between any two sb.
+ *
+ * In any case, we call do_splice_direct() and not splice_file_range(),
+ * without file_start_write() held, to avoid possible deadlocks related
+ * to splicing from input file, while file_start_write() is held on
+ * the output file on a different sb.
*/
- ret = generic_copy_file_range(file_in, pos_in, file_out, pos_out, len,
- flags);
-
+ ret = do_splice_direct(file_in, &pos_in, file_out, &pos_out,
+ min_t(size_t, len, MAX_RW_COUNT), 0);
done:
if (ret > 0) {
fsnotify_access(file_in);
@@ -1581,8 +1593,6 @@ ssize_t vfs_copy_file_range(struct file *file_in, loff_t pos_in,
inc_syscr(current);
inc_syscw(current);
- file_end_write(file_out);
-
return ret;
}
EXPORT_SYMBOL(vfs_copy_file_range);
--
2.34.1
