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authorRich Felker <dalias@libc.org>2015-12-09 19:37:53 +0000
committerRich Felker <dalias@libc.org>2016-04-28 20:47:50 +0000
commit511bc46f2afc11ccb966c65391fe6488e82d05b9 (patch)
tree49b53c729226f470c292651720d74dd47c33951b
parent09facf50a3243f5ea54c863a22f2b1f4ca6b0376 (diff)
downloadlinux-sh-511bc46f2afc11ccb966c65391fe6488e82d05b9.tar.gz
ramfs: fix VM_MAYSHARE mappings for NOMMU
The nommu do_mmap expects f_op->get_unmapped_area to either succeed or return -ENOSYS for VM_MAYSHARE (e.g. private read-only) mappings. Returning addr in the non-MAP_SHARED case was completely wrong, and only happened to work because addr was 0. However, it prevented VM_MAYSHARE mappings from sharing backing with the fs cache, and forced such mappings (including shareable program text) to be copied whenever the number of mappings transitioned from 0 to 1, impacting performance and memory usage. Subsequent mappings beyond the first still correctly shared memory with the first. Instead, treat VM_MAYSHARE identically to VM_SHARED at the file ops level; do_mmap already handles the semantic differences between them. Signed-off-by: Rich Felker <dalias@libc.org>
-rw-r--r--fs/ramfs/file-nommu.c8
1 files changed, 2 insertions, 6 deletions
diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index a586467f6ff6..be3ddd189cd4 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -211,14 +211,11 @@ static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
struct page **pages = NULL, **ptr, *page;
loff_t isize;
- if (!(flags & MAP_SHARED))
- return addr;
-
/* the mapping mustn't extend beyond the EOF */
lpages = (len + PAGE_SIZE - 1) >> PAGE_SHIFT;
isize = i_size_read(inode);
- ret = -EINVAL;
+ ret = -ENOSYS;
maxpages = (isize + PAGE_SIZE - 1) >> PAGE_SHIFT;
if (pgoff >= maxpages)
goto out;
@@ -227,7 +224,6 @@ static unsigned long ramfs_nommu_get_unmapped_area(struct file *file,
goto out;
/* gang-find the pages */
- ret = -ENOMEM;
pages = kcalloc(lpages, sizeof(struct page *), GFP_KERNEL);
if (!pages)
goto out_free;
@@ -263,7 +259,7 @@ out:
*/
static int ramfs_nommu_mmap(struct file *file, struct vm_area_struct *vma)
{
- if (!(vma->vm_flags & VM_SHARED))
+ if (!(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
return -ENOSYS;
file_accessed(file);