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MDEV-33543 Server hang caused by InnoDB change buffer

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Issue: When getting a page (buf_page_get_gen) with no latch option
(RW_NO_LATCH), the caller is not expected to follow the B-tree latching
order. However in buf_page_get_low we try to acquire shared page latch
unconditionally to wait for a page that is being loaded by another
thread concurrently. In general it could lead to latch order violation
and deadlock.

Currently it affects the change buffer insert path btr_latch_prev()
which tries to load the previous page out of order with RW_NO_LATCH and
two concurrent inserts into IBUF tree cause deadlock. This problem is
introduced in 10.6 by following commit.
commit 9436c778c3adba7c29dab5649668433d71e086f2 (MDEV-27058)

Fix: While trying to latch a page with RW_NO_LATCH, always use the
"*lock_try" interface and retry operation on failure after unfixing the
page.
This commit is contained in:
mariadb-DebarunBanerjee 2024-04-30 16:55:27 +05:30
parent 156761db3b
commit 90b95c6149
1 changed files with 12 additions and 3 deletions
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15
storage/innobase/buf/buf0buf.cc
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@ -2579,7 +2579,15 @@ ignore_unfixed:
in buf_page_t::read_complete() or
buf_pool_t::corrupted_evict(), or
after buf_zip_decompress() in this function. */
block->page.lock.s_lock();
if (rw_latch != RW_NO_LATCH) {
block->page.lock.s_lock();
} else if (!block->page.lock.s_lock_try()) {
/* For RW_NO_LATCH, we should not try to acquire S or X
latch directly as we could be violating the latching
order resulting in deadlock. Instead we try latching the
page and retry in case of a failure. */
goto wait_for_read;
}
state = block->page.state();
ut_ad(state < buf_page_t::READ_FIX
|| state >= buf_page_t::WRITE_FIX);
@ -2587,15 +2595,15 @@ ignore_unfixed:
block->page.lock.s_unlock();
if (UNIV_UNLIKELY(state < buf_page_t::UNFIXED)) {
block->page.unfix();
if (UNIV_UNLIKELY(id == page_id)) {
/* The page read was completed, and
another thread marked the page as free
while we were waiting. */
goto ignore_unfixed;
goto ignore_block;
}
ut_ad(id == page_id_t{~0ULL});
block->page.unfix();
if (++retries < BUF_PAGE_READ_MAX_RETRIES) {
goto loop;
@ -2634,6 +2642,7 @@ free_unfixed_block:
if (UNIV_UNLIKELY(!block->page.frame)) {
if (!block->page.lock.x_lock_try()) {
wait_for_unzip:
wait_for_read:
/* The page is being read or written, or
another thread is executing buf_zip_decompress()
in buf_page_get_low() on it. */