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authorLinus Torvalds <torvalds@linux-foundation.org>2019-03-15 18:26:07 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2019-03-15 18:26:07 (GMT)
commit8b0f9fa2e02dc95216577c3387b0707c5f60fbaf (patch)
tree8cb433d3c8ae7ecf8bf64dcb69dbfff2b350afa1
parent6b4c9f4469819a0c1a38a0a4541337e0f9bf6c11 (diff)
filemap: add a comment about FAULT_FLAG_RETRY_NOWAIT behavior
I thought Josef Bacik's patch to drop the mmap_sem was buggy, because when looking at the error cases, there was one case where we returned VM_FAULT_RETRY without actually dropping the mmap_sem. Josef had to explain to me (using small words) that yes, that's actually what we're supposed to do, and his patch was correct. Which not only convinced me he knew what he was doing and I should stop arguing with him, but also that I should add a comment to the case I was confused about. Patiently-pointed-out-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/filemap.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 2815cb7..d78f577 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2428,6 +2428,11 @@ static int lock_page_maybe_drop_mmap(struct vm_fault *vmf, struct page *page,
if (trylock_page(page))
return 1;
+ /*
+ * NOTE! This will make us return with VM_FAULT_RETRY, but with
+ * the mmap_sem still held. That's how FAULT_FLAG_RETRY_NOWAIT
+ * is supposed to work. We have way too many special cases..
+ */
if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
return 0;

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