Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.5
Description
A change in MDEV-23855 introduced a regression for MemorySanitizer: the doublewrite buffer would write uninitialized data to the file.
I did not find out why exactly that commit introduced the failure, but the fix is simple:
diff --git a/storage/innobase/buf/buf0dblwr.cc b/storage/innobase/buf/buf0dblwr.cc
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index a8ae3e2782a..c14634ae229 100644
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--- a/storage/innobase/buf/buf0dblwr.cc
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+++ b/storage/innobase/buf/buf0dblwr.cc
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@@ -736,7 +736,8 @@ void buf_dblwr_t::add_to_batch(const IORequest &request, size_t size)
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encryption and/or page compression */
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void *frame= buf_page_get_frame(request.bpage);
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- memcpy_aligned<OS_FILE_LOG_BLOCK_SIZE>(p, frame, size);
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+ memcpy_aligned<256>(p, frame, size); /* fil_page_compress() guarantee */
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+ memset_aligned<256>(p + size, 0, srv_page_size - size);
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ut_ad(!request.bpage->zip_size() || request.bpage->zip_size() == size);
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ut_ad(active_slot->reserved == active_slot->first_free);
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ut_ad(active_slot->reserved < buf_size); |
This is also correcting the alignment assertion. fil_page_compress() for page_compressed pages is only guaranteeing 256-byte alignment, not 512 bytes. For ROW_FORMAT=COMPRESSED pages, the minimum alignment is 1024 bytes.
Attachments
Issue Links
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- Closed
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It turns out that the alignment assumptions in memcpy_aligned and memset_aligned do not cover the size, but only the pointers. Hence, the 512-byte alignment of the existing call is not incorrect, but only inaccurate. I would propose an improved patch:
diff --git a/storage/innobase/buf/buf0dblwr.cc b/storage/innobase/buf/buf0dblwr.ccindex a8ae3e2782a..284936ddc43 100644--- a/storage/innobase/buf/buf0dblwr.cc+++ b/storage/innobase/buf/buf0dblwr.cc@@ -736,7 +736,11 @@ void buf_dblwr_t::add_to_batch(const IORequest &request, size_t size)encryption and/or page compression */void *frame= buf_page_get_frame(request.bpage);- memcpy_aligned<OS_FILE_LOG_BLOCK_SIZE>(p, frame, size);+ /* "frame" is at least 1024-byte aligned for ROW_FORMAT=COMPRESSED pages,+ and at least srv_page_size (4096-byte) for everything else. */+ memcpy_aligned<UNIV_ZIP_SIZE_MIN>(p, frame, size);+ /* fil_page_compress() for page_compressed guarantees 256-byte alignment */+ memset_aligned<256>(p + size, 0, srv_page_size - size);ut_ad(!request.bpage->zip_size() || request.bpage->zip_size() == size);ut_ad(active_slot->reserved == active_slot->first_free);