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| author | Keith Bostic <keith.bostic@mongodb.com> | 2016-06-26 22:45:12 -0400 |
|---|---|---|
| committer | Alex Gorrod <alexander.gorrod@mongodb.com> | 2016-06-28 14:32:57 +1000 |
| commit | 552a33b5bdb4f4d6e561c603a33ccb58a7ee9eca (patch) | |
| tree | 3281eaed6b6c066613d144efb1bd5a132e10d8d3 | |
| parent | 9cfe4e14acc569a313fd7d7781ac036b82269020 (diff) | |
| download | mongo-552a33b5bdb4f4d6e561c603a33ccb58a7ee9eca.tar.gz | |
WT-2708 split child-update race with reconciliation/eviction (#2835)
(cherry picked from commit 521270d54c41294da86a95690a54068cc23d4f1d)
When splitting the root page and updating the child's WT_REF.addr, reconciliation/eviction can race with us, updating WT_REF.addr after our read and before our update. The update is necessary because the child's
address points into the page being split: if the address changes, then it can no longer point into the page being split and the update is no longer necessary.
| -rw-r--r-- | src/btree/bt_split.c | 23 |
1 files changed, 16 insertions, 7 deletions
diff --git a/src/btree/bt_split.c b/src/btree/bt_split.c index 7f3620bb361..39c10133542 100644 --- a/src/btree/bt_split.c +++ b/src/btree/bt_split.c @@ -251,7 +251,7 @@ static int __split_ref_deepen_move(WT_SESSION_IMPL *session, WT_PAGE *parent, WT_REF *ref, size_t *parent_decrp, size_t *child_incrp) { - WT_ADDR *addr; + WT_ADDR *addr, *ref_addr; WT_CELL_UNPACK unpack; WT_DECL_RET; WT_IKEY *ikey; @@ -287,13 +287,18 @@ __split_ref_deepen_move(WT_SESSION_IMPL *session, } /* - * If there's no address (the page has never been written), or the - * address has been instantiated, there's no work to do. Otherwise, - * get the address from the on-page cell. + * If there's no address at all (the page has never been written), or + * the address has already been instantiated, there's no work to do. + * Otherwise, the address still references a split page on-page cell, + * instantiate it. We can race with reconciliation and/or eviction of + * the child pages, be cautious: read the address and verify it, and + * only update it if the value is unchanged from the original. In the + * case of a race, the address must no longer reference the split page, + * we're done. */ - addr = ref->addr; - if (addr != NULL && !__wt_off_page(parent, addr)) { - __wt_cell_unpack((WT_CELL *)ref->addr, &unpack); + WT_ORDERED_READ(ref_addr, ref->addr); + if (ref_addr != NULL && !__wt_off_page(parent, ref_addr)) { + __wt_cell_unpack((WT_CELL *)ref_addr, &unpack); WT_RET(__wt_calloc_one(session, &addr)); if ((ret = __wt_strndup( session, unpack.data, unpack.size, &addr->addr)) != 0) { @@ -304,6 +309,10 @@ __split_ref_deepen_move(WT_SESSION_IMPL *session, addr->type = unpack.raw == WT_CELL_ADDR_INT ? WT_ADDR_INT : WT_ADDR_LEAF; ref->addr = addr; + if (!__wt_atomic_cas_ptr(&ref->addr, ref_addr, addr)) { + __wt_free(session, addr->addr); + __wt_free(session, addr); + } } /* And finally, the WT_REF itself. */ |