During our tests in containers, there is a read-only file (i.e., shared
libraies) in the overlayfs filesystem, and the underlying filesystem is
ext4, which supports large folio. We mmap the file with PROT_READ prot,
and then call madvise(MADV_COLLAPSE) for it. However, the madvise call
fails and returns EINVAL.
The reason is that the mapping address isn't aligned to PMD size. Since
overlayfs doesn't support large folio, __get_unmapped_area() doesn't call
thp_get_unmapped_area() to get a THP aligned address.
To fix it, call get_unmapped_area() with the realfile.
Besides, since overlayfs may be built with CONFIG_OVERLAY_FS=m, we should
export get_unmapped_area().
Signed-off-by: Jinjiang Tu <tujinjiang@xxxxxxxxxx>
---
fs/overlayfs/file.c | 20 ++++++++++++++++++++
mm/mmap.c | 1 +
2 files changed, 21 insertions(+)
diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 969b458100fe..d0dcf675ebe8 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -653,6 +653,25 @@ static int ovl_flush(struct file *file, fl_owner_t id)
return err;
}
+static unsigned long ovl_get_unmapped_area(struct file *file,
+ unsigned long addr, unsigned long len, unsigned long pgoff,
+ unsigned long flags)
+{
+ struct file *realfile;
+ const struct cred *old_cred;
+ unsigned long ret;
+
+ realfile = ovl_real_file(file);
+ if (IS_ERR(realfile))
+ return PTR_ERR(realfile);
+
+ old_cred = ovl_override_creds(file_inode(file)->i_sb);
+ ret = get_unmapped_area(realfile, addr, len, pgoff, flags);
+ ovl_revert_creds(old_cred);
+
+ return ret;
+}
+
const struct file_operations ovl_file_operations = {
.open = ovl_open,
.release = ovl_release,
@@ -661,6 +680,7 @@ const struct file_operations ovl_file_operations = {
.write_iter = ovl_write_iter,
.fsync = ovl_fsync,
.mmap = ovl_mmap,
+ .get_unmapped_area = ovl_get_unmapped_area,
.fallocate = ovl_fallocate,
.fadvise = ovl_fadvise,
.flush = ovl_flush,
diff --git a/mm/mmap.c b/mm/mmap.c
index 16f8e8be01f8..60eb1ff7c9a8 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -913,6 +913,7 @@ __get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
error = security_mmap_addr(addr);
return error ? error : addr;
}
+EXPORT_SYMBOL(__get_unmapped_area);
unsigned long
mm_get_unmapped_area(struct mm_struct *mm, struct file *file,
--
2.34.1
