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mm: describe mmap_sem rules for __lock_page_or_retry() and callers

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Add a comment describing the circumstances in which
__lock_page_or_retry() will or will not release the mmap_sem when
returning 0.

Add comments to lock_page_or_retry()'s callers (filemap_fault(),
do_swap_page()) noting the impact on VM_FAULT_RETRY returns.

Add comments on up the call tree, particularly replacing the false "We
return with mmap_sem still held" comments.

Signed-off-by: Paul Cassella <cassella@cray.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Paul Cassella 2014-08-06 16:07:24 -07:00 • committed by Linus Torvalds
parent 4ffeaf3560
commit 9a95f3cf7b
6 changed files with 82 additions and 8 deletions
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3
include/linux/pagemap.h
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@ -484,6 +484,9 @@ static inline int lock_page_killable(struct page *page)
/*
* lock_page_or_retry - Lock the page, unless this would block and the
* caller indicated that it can handle a retry.
*
* Return value and mmap_sem implications depend on flags; see
* __lock_page_or_retry().
*/
static inline int lock_page_or_retry(struct page *page, struct mm_struct *mm,
unsigned int flags)