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ZIL: Fix config lock deadlock. #15080

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Jul 24, 2023
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ZIL: Fix config lock deadlock. #15080

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34 changes: 27 additions & 7 deletions module/zfs/zil.c
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Original file line number Diff line number Diff line change
Expand Up @@ -151,6 +151,7 @@ static kmem_cache_t *zil_lwb_cache;
static kmem_cache_t *zil_zcw_cache;

static void zil_lwb_commit(zilog_t *zilog, lwb_t *lwb, itx_t *itx);
static void zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb);
static itx_t *zil_itx_clone(itx_t *oitx);

static int
Expand Down Expand Up @@ -1768,7 +1769,7 @@ static uint_t zil_maxblocksize = SPA_OLD_MAXBLOCKSIZE;
* Has to be called under zl_issuer_lock to chain more lwbs.
*/
static lwb_t *
zil_lwb_write_close(zilog_t *zilog, lwb_t *lwb)
zil_lwb_write_close(zilog_t *zilog, lwb_t *lwb, list_t *ilwbs)
{
lwb_t *nlwb = NULL;
zil_chain_t *zilc;
Expand Down Expand Up @@ -1870,6 +1871,27 @@ zil_lwb_write_close(zilog_t *zilog, lwb_t *lwb)

dmu_tx_commit(tx);

/*
* We need to acquire the config lock for the lwb to issue it later.
* However, if we already have a queue of closed parent lwbs already
* holding the config lock (but not yet issued), we can't block here
* waiting on the lock or we will deadlock. In that case we must
* first issue to parent IOs before waiting on the lock.
*/
if (ilwbs && !list_is_empty(ilwbs)) {
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if (!spa_config_tryenter(spa, SCL_STATE, lwb, RW_READER)) {
lwb_t *tlwb;
while ((tlwb = list_remove_head(ilwbs)) != NULL)
zil_lwb_write_issue(zilog, tlwb);
spa_config_enter(spa, SCL_STATE, lwb, RW_READER);
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}
} else {
spa_config_enter(spa, SCL_STATE, lwb, RW_READER);
}

if (ilwbs)
list_insert_tail(ilwbs, lwb);

/*
* If there was an allocation failure then nlwb will be null which
* forces a txg_wait_synced().
Expand Down Expand Up @@ -1933,7 +1955,7 @@ zil_lwb_write_issue(zilog_t *zilog, lwb_t *lwb)
ZIL_STAT_INCR(zilog, zil_itx_metaslab_normal_alloc,
BP_GET_LSIZE(&lwb->lwb_blk));
}
spa_config_enter(zilog->zl_spa, SCL_STATE, lwb, RW_READER);
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ASSERT(spa_config_held(zilog->zl_spa, SCL_STATE, RW_READER));
zil_lwb_add_block(lwb, &lwb->lwb_blk);
lwb->lwb_issued_timestamp = gethrtime();
zio_nowait(lwb->lwb_root_zio);
Expand Down Expand Up @@ -2037,8 +2059,7 @@ zil_lwb_assign(zilog_t *zilog, lwb_t *lwb, itx_t *itx, list_t *ilwbs)
lwb_sp < zil_max_waste_space(zilog) &&
(dlen % max_log_data == 0 ||
lwb_sp < reclen + dlen % max_log_data))) {
list_insert_tail(ilwbs, lwb);
lwb = zil_lwb_write_close(zilog, lwb);
lwb = zil_lwb_write_close(zilog, lwb, ilwbs);
if (lwb == NULL)
return (NULL);
zil_lwb_write_open(zilog, lwb);
Expand Down Expand Up @@ -2937,8 +2958,7 @@ zil_process_commit_list(zilog_t *zilog, zil_commit_waiter_t *zcw, list_t *ilwbs)
zfs_commit_timeout_pct / 100;
if (sleep < zil_min_commit_timeout ||
lwb->lwb_sz - lwb->lwb_nused < lwb->lwb_sz / 8) {
list_insert_tail(ilwbs, lwb);
lwb = zil_lwb_write_close(zilog, lwb);
lwb = zil_lwb_write_close(zilog, lwb, ilwbs);
zilog->zl_cur_used = 0;
if (lwb == NULL) {
while ((lwb = list_remove_head(ilwbs))
Expand Down Expand Up @@ -3096,7 +3116,7 @@ zil_commit_waiter_timeout(zilog_t *zilog, zil_commit_waiter_t *zcw)
* since we've reached the commit waiter's timeout and it still
* hasn't been issued.
*/
lwb_t *nlwb = zil_lwb_write_close(zilog, lwb);
lwb_t *nlwb = zil_lwb_write_close(zilog, lwb, NULL);

ASSERT3S(lwb->lwb_state, !=, LWB_STATE_OPENED);

Expand Down