From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751705AbeEKAkr (ORCPT ); Thu, 10 May 2018 20:40:47 -0400 Received: from mx2.suse.de ([195.135.220.15]:37370 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750751AbeEKAko (ORCPT ); Thu, 10 May 2018 20:40:44 -0400 From: NeilBrown To: Oleg Drokin , Andreas Dilger , James Simmons Date: Fri, 11 May 2018 10:37:14 +1000 Subject: [PATCH 1/6] staging: lustre: make key_set_version an atomic_t Cc: Linux Kernel Mailing List , Lustre Development List Message-ID: <152599903422.19824.6448081685151609850.stgit@noble> In-Reply-To: <152599874625.19824.11344372150811845854.stgit@noble> References: <152599874625.19824.11344372150811845854.stgit@noble> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As a first step to simplifying the locking in lu_object.c, change key_set_version to an atomic_t. This will mean we don't need to hold a spinlock when incrementing. It is clear that keys_fill() (and so lu_context_refill()) cannot race with itself as it holds no locks for the main part of the work. So updates to lc_version, and testing of that value cannot need locking either. So remove the locking from keys_fill() and lu_context_refill() as there is no longer anything to protect. The locking around lu_keys_initing_cnt is preserved for now. Also, don't increment when deregistering or quiescing a key. key_set_version is *only* use to avoid filling new key values if there have been no changes to the set of key. Deregistering a key does not mean that we need to try filling any new value, so the increment is pointless. Finally, remove the refill loop in keys_fill(). If a key is registered or revived while keys_fill() is running it must be safe to ignore it just as we would if it was registered immediately after keys_fill() ran. The important thing is that the keys_set_version stored in ctx->lc_version must be sampled *before* those unseen keys were added. So sample keys_set_version early. Signed-off-by: NeilBrown --- drivers/staging/lustre/lustre/obdclass/lu_object.c | 26 ++++---------------- 1 file changed, 5 insertions(+), 21 deletions(-) diff --git a/drivers/staging/lustre/lustre/obdclass/lu_object.c b/drivers/staging/lustre/lustre/obdclass/lu_object.c index f14e3509f059..b38adf75e8e4 100644 --- a/drivers/staging/lustre/lustre/obdclass/lu_object.c +++ b/drivers/staging/lustre/lustre/obdclass/lu_object.c @@ -1329,7 +1329,7 @@ static atomic_t lu_key_initing_cnt = ATOMIC_INIT(0); * lu_context_refill(). No locking is provided, as initialization and shutdown * are supposed to be externally serialized. */ -static unsigned int key_set_version; +static atomic_t key_set_version = ATOMIC_INIT(0); /** * Register new key. @@ -1352,7 +1352,7 @@ int lu_context_key_register(struct lu_context_key *key) lu_keys[i] = key; lu_ref_init(&key->lct_reference); result = 0; - ++key_set_version; + atomic_inc(&key_set_version); break; } } @@ -1390,7 +1390,6 @@ void lu_context_key_degister(struct lu_context_key *key) lu_context_key_quiesce(key); write_lock(&lu_keys_guard); - ++key_set_version; key_fini(&lu_shrink_env.le_ctx, key->lct_index); /** @@ -1550,7 +1549,6 @@ void lu_context_key_quiesce(struct lu_context_key *key) list_for_each_entry(ctx, &lu_context_remembered, lc_remember) key_fini(ctx, key->lct_index); - ++key_set_version; write_unlock(&lu_keys_guard); } } @@ -1559,7 +1557,7 @@ void lu_context_key_revive(struct lu_context_key *key) { write_lock(&lu_keys_guard); key->lct_tags &= ~LCT_QUIESCENT; - ++key_set_version; + atomic_inc(&key_set_version); write_unlock(&lu_keys_guard); } @@ -1579,7 +1577,6 @@ static void keys_fini(struct lu_context *ctx) static int keys_fill(struct lu_context *ctx) { - unsigned int pre_version; unsigned int i; /* @@ -1593,10 +1590,9 @@ static int keys_fill(struct lu_context *ctx) */ read_lock(&lu_keys_guard); atomic_inc(&lu_key_initing_cnt); - pre_version = key_set_version; read_unlock(&lu_keys_guard); + ctx->lc_version = atomic_read(&key_set_version); -refill: LINVRNT(ctx->lc_value); for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) { struct lu_context_key *key; @@ -1639,15 +1635,7 @@ static int keys_fill(struct lu_context *ctx) } } - read_lock(&lu_keys_guard); - if (pre_version != key_set_version) { - pre_version = key_set_version; - read_unlock(&lu_keys_guard); - goto refill; - } - ctx->lc_version = key_set_version; atomic_dec(&lu_key_initing_cnt); - read_unlock(&lu_keys_guard); return 0; } @@ -1756,13 +1744,9 @@ EXPORT_SYMBOL(lu_context_exit); */ int lu_context_refill(struct lu_context *ctx) { - read_lock(&lu_keys_guard); - if (likely(ctx->lc_version == key_set_version)) { - read_unlock(&lu_keys_guard); + if (likely(ctx->lc_version == atomic_read(&key_set_version))) return 0; - } - read_unlock(&lu_keys_guard); return keys_fill(ctx); }