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ctdb_client: fix race in starting concurrent transactions on a single node

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There are two races in concurrent transactions on a single node.
One in starting a transaction, and one with committing (replaying).

This commit closes the first race by storing the pid in the
transaction-lock record and comparing the own pid against it
as a measure to prevent starting a second transaction when
a second node has come inbetween and changed the pid in the lock
record.

Michael

(This used to be ctdb commit 84e5a55a900b01903b80e23045edfc726d8d77a1)
This commit is contained in:
Michael Adam 2009-08-04 09:45:50 +02:00
parent eb305efdb0
commit 3cb4bcd211
1 changed files with 24 additions and 1 deletions
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25
ctdb/client/ctdb_client.c
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@ -3107,11 +3107,13 @@ static int ctdb_transaction_fetch_start(struct ctdb_transaction_handle *h)
{
struct ctdb_record_handle *rh;
TDB_DATA key;
TDB_DATA data;
struct ctdb_ltdb_header header;
TALLOC_CTX *tmp_ctx;
const char *keyname = CTDB_TRANSACTION_LOCK_KEY;
int ret;
struct ctdb_db_context *ctdb_db = h->ctdb_db;
pid_t pid;
key.dptr = discard_const(keyname);
key.dsize = strlen(keyname);
@ -3130,6 +3132,21 @@ again:
talloc_free(tmp_ctx);
return -1;
}
/*
* store the pid in the database:
* it is not enough that the node is dmaster...
*/
pid = getpid();
data.dptr = (unsigned char *)&pid;
data.dsize = sizeof(pid_t);
ret = ctdb_ltdb_store(ctdb_db, key, &(rh->header), data);
if (ret != 0) {
DEBUG(DEBUG_ERR, (__location__ " Failed to store pid in "
"transaction record\n"));
talloc_free(tmp_ctx);
return -1;
}
talloc_free(rh);
ret = tdb_transaction_start(ctdb_db->ltdb->tdb);
@ -3139,13 +3156,19 @@ again:
return -1;
}
ret = ctdb_ltdb_fetch(ctdb_db, key, &header, tmp_ctx, NULL);
ret = ctdb_ltdb_fetch(ctdb_db, key, &header, tmp_ctx, &data);
if (ret != 0 || header.dmaster != ctdb_db->ctdb->pnn) {
tdb_transaction_cancel(ctdb_db->ltdb->tdb);
talloc_free(tmp_ctx);
goto again;
}
if ((data.dsize != sizeof(pid_t)) || (*(pid_t *)(data.dptr) != pid)) {
tdb_transaction_cancel(ctdb_db->ltdb->tdb);
talloc_free(tmp_ctx);
goto again;
}
talloc_free(tmp_ctx);
return 0;