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-rw-r--r--include/linux/pagemap.h11
-rw-r--r--mm/filemap.c122
2 files changed, 112 insertions, 21 deletions
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 862fc07dc6c0..8f1e390fd71b 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -219,6 +219,9 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
{
int ret;
+ if (unlikely(size == 0))
+ return 0;
+
/*
* Writing zeroes into userspace here is OK, because we know that if
* the zero gets there, we'll be overwriting it.
@@ -238,19 +241,23 @@ static inline int fault_in_pages_writeable(char __user *uaddr, int size)
return ret;
}
-static inline void fault_in_pages_readable(const char __user *uaddr, int size)
+static inline int fault_in_pages_readable(const char __user *uaddr, int size)
{
volatile char c;
int ret;
+ if (unlikely(size == 0))
+ return 0;
+
ret = __get_user(c, uaddr);
if (ret == 0) {
const char __user *end = uaddr + size - 1;
if (((unsigned long)uaddr & PAGE_MASK) !=
((unsigned long)end & PAGE_MASK))
- __get_user(c, end);
+ ret = __get_user(c, end);
}
+ return ret;
}
#endif /* _LINUX_PAGEMAP_H */
diff --git a/mm/filemap.c b/mm/filemap.c
index c59d5b3cd99a..557fd887254f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1826,11 +1826,12 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
filemap_set_next_iovec(&cur_iov, nr_segs, &iov_offset, written);
do {
+ struct page *src_page;
struct page *page;
pgoff_t index; /* Pagecache index for current page */
unsigned long offset; /* Offset into pagecache page */
- unsigned long maxlen; /* Bytes remaining in current iovec */
- size_t bytes; /* Bytes to write to page */
+ unsigned long seglen; /* Bytes remaining in current iovec */
+ unsigned long bytes; /* Bytes to write to page */
size_t copied; /* Bytes copied from user */
buf = cur_iov->iov_base + iov_offset;
@@ -1840,20 +1841,30 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
if (bytes > count)
bytes = count;
- maxlen = cur_iov->iov_len - iov_offset;
- if (maxlen > bytes)
- maxlen = bytes;
+ /*
+ * a non-NULL src_page indicates that we're doing the
+ * copy via get_user_pages and kmap.
+ */
+ src_page = NULL;
+
+ seglen = cur_iov->iov_len - iov_offset;
+ if (seglen > bytes)
+ seglen = bytes;
-#ifndef CONFIG_DEBUG_VM
/*
* Bring in the user page that we will copy from _first_.
* Otherwise there's a nasty deadlock on copying from the
* same page as we're writing to, without it being marked
* up-to-date.
+ *
+ * Not only is this an optimisation, but it is also required
+ * to check that the address is actually valid, when atomic
+ * usercopies are used, below.
*/
- fault_in_pages_readable(buf, maxlen);
-#endif
-
+ if (unlikely(fault_in_pages_readable(buf, seglen))) {
+ status = -EFAULT;
+ break;
+ }
page = __grab_cache_page(mapping, index);
if (!page) {
@@ -1861,32 +1872,104 @@ generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
break;
}
+ /*
+ * non-uptodate pages cannot cope with short copies, and we
+ * cannot take a pagefault with the destination page locked.
+ * So pin the source page to copy it.
+ */
+ if (!PageUptodate(page)) {
+ unlock_page(page);
+
+ src_page = alloc_page(GFP_KERNEL);
+ if (!src_page) {
+ page_cache_release(page);
+ status = -ENOMEM;
+ break;
+ }
+
+ /*
+ * Cannot get_user_pages with a page locked for the
+ * same reason as we can't take a page fault with a
+ * page locked (as explained below).
+ */
+ copied = filemap_copy_from_user(src_page, offset,
+ cur_iov, nr_segs, iov_offset, bytes);
+ if (unlikely(copied == 0)) {
+ status = -EFAULT;
+ page_cache_release(page);
+ page_cache_release(src_page);
+ break;
+ }
+ bytes = copied;
+
+ lock_page(page);
+ /*
+ * Can't handle the page going uptodate here, because
+ * that means we would use non-atomic usercopies, which
+ * zero out the tail of the page, which can cause
+ * zeroes to become transiently visible. We could just
+ * use a non-zeroing copy, but the APIs aren't too
+ * consistent.
+ */
+ if (unlikely(!page->mapping || PageUptodate(page))) {
+ unlock_page(page);
+ page_cache_release(page);
+ page_cache_release(src_page);
+ continue;
+ }
+
+ }
+
status = a_ops->prepare_write(file, page, offset, offset+bytes);
if (unlikely(status))
goto fs_write_aop_error;
- copied = filemap_copy_from_user(page, offset,
+ if (!src_page) {
+ /*
+ * Must not enter the pagefault handler here, because
+ * we hold the page lock, so we might recursively
+ * deadlock on the same lock, or get an ABBA deadlock
+ * against a different lock, or against the mmap_sem
+ * (which nests outside the page lock). So increment
+ * preempt count, and use _atomic usercopies.
+ *
+ * The page is uptodate so we are OK to encounter a
+ * short copy: if unmodified parts of the page are
+ * marked dirty and written out to disk, it doesn't
+ * really matter.
+ */
+ pagefault_disable();
+ copied = filemap_copy_from_user_atomic(page, offset,
cur_iov, nr_segs, iov_offset, bytes);
+ pagefault_enable();
+ } else {
+ void *src, *dst;
+ src = kmap_atomic(src_page, KM_USER0);
+ dst = kmap_atomic(page, KM_USER1);
+ memcpy(dst + offset, src + offset, bytes);
+ kunmap_atomic(dst, KM_USER1);
+ kunmap_atomic(src, KM_USER0);
+ copied = bytes;
+ }
flush_dcache_page(page);
status = a_ops->commit_write(file, page, offset, offset+bytes);
if (unlikely(status < 0 || status == AOP_TRUNCATED_PAGE))
goto fs_write_aop_error;
- if (unlikely(copied != bytes)) {
- status = -EFAULT;
- goto fs_write_aop_error;
- }
if (unlikely(status > 0)) /* filesystem did partial write */
- copied = status;
+ copied = min_t(size_t, copied, status);
+
+ unlock_page(page);
+ mark_page_accessed(page);
+ page_cache_release(page);
+ if (src_page)
+ page_cache_release(src_page);
written += copied;
count -= copied;
pos += copied;
filemap_set_next_iovec(&cur_iov, nr_segs, &iov_offset, copied);
- unlock_page(page);
- mark_page_accessed(page);
- page_cache_release(page);
balance_dirty_pages_ratelimited(mapping);
cond_resched();
continue;
@@ -1895,6 +1978,8 @@ fs_write_aop_error:
if (status != AOP_TRUNCATED_PAGE)
unlock_page(page);
page_cache_release(page);
+ if (src_page)
+ page_cache_release(src_page);
/*
* prepare_write() may have instantiated a few blocks
@@ -1907,7 +1992,6 @@ fs_write_aop_error:
continue;
else
break;
-
} while (count);
*ppos = pos;
generated by cgit v1.2.3 (git 2.39.1) at 2024-12-15 06:35:38 +0100