diff options
| author | Brian Behlendorf <[email protected]> | 2013-04-25 16:29:22 -0700 |
|---|---|---|
| committer | Brian Behlendorf <[email protected]> | 2013-04-26 14:42:36 -0700 |
| commit | 57f5a2008e2e6acf58934cf43c5fdca0faffa73e (patch) | |
| tree | 6097764cffc614760d918d844479d85414c84075 /module | |
| parent | 0c15bf16f1050e710cad1783d15eea63cca792c0 (diff) | |
Fix txg_quiesce thread deadlock
A deadlock was accidentally introduced by commit e95853a which
can occur when the system is under memory pressure. What happens
is that while the txg_quiesce thread is holding the tx->tx_cpu
locks it enters memory reclaim. In the context of this memory
reclaim it then issues synchronous I/O to a ZVOL swap device.
Because the txg_quiesce thread is holding the tx->tx_cpu locks
a new txg cannot be opened to handle the I/O. Deadlock.
The fix is straight forward. Move the memory allocation outside
the critical region where the tx->tx_cpu locks are held. And for
good measure change the offending allocation to KM_PUSHPAGE to
ensure it never attempts to issue I/O during reclaim.
Signed-off-by: Brian Behlendorf <[email protected]>
Issue #1274
Diffstat (limited to 'module')
| -rw-r--r-- | module/zfs/dsl_pool.c | 2 | ||||
| -rw-r--r-- | module/zfs/txg.c | 14 |
2 files changed, 8 insertions, 8 deletions
diff --git a/module/zfs/dsl_pool.c b/module/zfs/dsl_pool.c index 704f034e9..771b265c2 100644 --- a/module/zfs/dsl_pool.c +++ b/module/zfs/dsl_pool.c @@ -143,7 +143,7 @@ dsl_pool_txg_history_add(dsl_pool_t *dp, uint64_t txg) { txg_history_t *th, *rm; - th = kmem_zalloc(sizeof(txg_history_t), KM_SLEEP); + th = kmem_zalloc(sizeof(txg_history_t), KM_PUSHPAGE); mutex_init(&th->th_lock, NULL, MUTEX_DEFAULT, NULL); th->th_kstat.txg = txg; th->th_kstat.state = TXG_STATE_OPEN; diff --git a/module/zfs/txg.c b/module/zfs/txg.c index c7c3df3f8..7c820af4f 100644 --- a/module/zfs/txg.c +++ b/module/zfs/txg.c @@ -367,6 +367,13 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg) tx->tx_open_txg++; /* + * Now that we've incremented tx_open_txg, we can let threads + * enter the next transaction group. + */ + for (c = 0; c < max_ncpus; c++) + mutex_exit(&tx->tx_cpu[c].tc_lock); + + /* * Measure how long the txg was open and replace the kstat. */ th = dsl_pool_txg_history_get(dp, txg); @@ -376,13 +383,6 @@ txg_quiesce(dsl_pool_t *dp, uint64_t txg) dsl_pool_txg_history_add(dp, tx->tx_open_txg); /* - * Now that we've incremented tx_open_txg, we can let threads - * enter the next transaction group. - */ - for (c = 0; c < max_ncpus; c++) - mutex_exit(&tx->tx_cpu[c].tc_lock); - - /* * Quiesce the transaction group by waiting for everyone to txg_exit(). */ start = gethrtime(); |