diff options
Diffstat (limited to 'mm/filemap.h')
| -rw-r--r-- | mm/filemap.h | 26 |
1 files changed, 18 insertions, 8 deletions
diff --git a/mm/filemap.h b/mm/filemap.h index 5683cde2205..536979fb4ba 100644 --- a/mm/filemap.h +++ b/mm/filemap.h @@ -16,15 +16,23 @@ #include <linux/uaccess.h> size_t -__filemap_copy_from_user_iovec(char *vaddr, - const struct iovec *iov, - size_t base, - size_t bytes); +__filemap_copy_from_user_iovec_inatomic(char *vaddr, + const struct iovec *iov, + size_t base, + size_t bytes); /* * Copy as much as we can into the page and return the number of bytes which * were sucessfully copied. If a fault is encountered then clear the page * out to (offset+bytes) and return the number of bytes which were copied. + * + * NOTE: For this to work reliably we really want copy_from_user_inatomic_nocache + * to *NOT* zero any tail of the buffer that it failed to copy. If it does, + * and if the following non-atomic copy succeeds, then there is a small window + * where the target page contains neither the data before the write, nor the + * data after the write (it contains zero). A read at this time will see + * data that is inconsistent with any ordering of the read and the write. + * (This has been detected in practice). */ static inline size_t filemap_copy_from_user(struct page *page, unsigned long offset, @@ -60,13 +68,15 @@ filemap_copy_from_user_iovec(struct page *page, unsigned long offset, size_t copied; kaddr = kmap_atomic(page, KM_USER0); - copied = __filemap_copy_from_user_iovec(kaddr + offset, iov, - base, bytes); + copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov, + base, bytes); kunmap_atomic(kaddr, KM_USER0); if (copied != bytes) { kaddr = kmap(page); - copied = __filemap_copy_from_user_iovec(kaddr + offset, iov, - base, bytes); + copied = __filemap_copy_from_user_iovec_inatomic(kaddr + offset, iov, + base, bytes); + if (bytes - copied) + memset(kaddr + offset + copied, 0, bytes - copied); kunmap(page); } return copied; |