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Thu, 26 Mar 2026 20:33:38 -0700 (PDT) From: Pasha Tatashin To: rppt@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, pasha.tatashin@soleen.com, dmatlack@google.com, pratyush@kernel.org, skhawaja@google.com Subject: [PATCH v3 02/10] liveupdate: Synchronize lazy initialization of FLB private state Date: Fri, 27 Mar 2026 03:33:26 +0000 Message-ID: <20260327033335.696621-3-pasha.tatashin@soleen.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260327033335.696621-1-pasha.tatashin@soleen.com> References: <20260327033335.696621-1-pasha.tatashin@soleen.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: m1ao7snc7hw1esfhb1bowghxkxehh7mw X-Rspamd-Queue-Id: 217ADA0007 X-Rspamd-Server: rspam09 X-HE-Tag: 1774582419-667957 X-HE-Meta: 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 iBOv88mL 5dos5Y2NZX1PIa0Z3yiIH4RnGx1rYb2vC4aa089N46eL07DOYPevDMkvxGhpzxpOHhnBwTPwKjYev9Z5GznR7E1eno7M0M3okAioHSz/stjVdo9z9seAU612Cr2Qz9gOk2/cqu0gjSdbMFOGM4d98UyAZhqkcByFKqF2NqyDoxbhiLp5nuLUjuC4VcynN6t2zkb0AcU6/UW0CKmh6AH/SrA8SNtmHN7idqBZc8/QoM3L6Skx1bLUvgh5ybXTv3EgIVV2JOIAOorjmpuKhdKJiyZhFiCmZqg6Js3B48LnGs0tCeE/yBqkc1SFi9SVHhwu3WZsPk9e7Fz7PdNA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: The luo_flb_get_private() function, which is responsible for lazily initializing the private state of FLB objects, can be called concurrently from multiple threads. This creates a data race on the 'initialized' flag and can lead to multiple executions of mutex_init() and INIT_LIST_HEAD() on the same memory. Introduce a static spinlock (luo_flb_init_lock) local to the function to synchronize the initialization path. Use smp_load_acquire() and smp_store_release() for memory ordering between the fast path and the slow path. Signed-off-by: Pasha Tatashin --- kernel/liveupdate/luo_flb.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/kernel/liveupdate/luo_flb.c b/kernel/liveupdate/luo_flb.c index 855af655b09b..317c02a94da5 100644 --- a/kernel/liveupdate/luo_flb.c +++ b/kernel/liveupdate/luo_flb.c @@ -89,13 +89,18 @@ struct luo_flb_link { static struct luo_flb_private *luo_flb_get_private(struct liveupdate_flb *flb) { struct luo_flb_private *private = &ACCESS_PRIVATE(flb, private); + static DEFINE_SPINLOCK(luo_flb_init_lock); + if (smp_load_acquire(&private->initialized)) + return private; + + guard(spinlock)(&luo_flb_init_lock); if (!private->initialized) { mutex_init(&private->incoming.lock); mutex_init(&private->outgoing.lock); INIT_LIST_HEAD(&private->list); private->users = 0; - private->initialized = true; + smp_store_release(&private->initialized, true); } return private; -- 2.43.0