diff options
| author | Rich Felker <dalias@libc.org> | 2015-12-09 19:37:53 +0000 |
|---|---|---|
| committer | Rich Felker <dalias@libc.org> | 2016-04-28 20:47:50 +0000 |
| commit | 511bc46f2afc11ccb966c65391fe6488e82d05b9 (patch) | |
| tree | 49b53c729226f470c292651720d74dd47c33951b | |
| parent | 09facf50a3243f5ea54c863a22f2b1f4ca6b0376 (diff) | |
| download | linux-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.c | 8 |
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); |