Commit c50d295c authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Paolo Abeni
Browse files

rds: Use nested-BH locking for rds_page_remainder 



rds_page_remainder is a per-CPU variable and relies on disabled BH for its
locking. Without per-CPU locking in local_bh_disable() on PREEMPT_RT
this data structure requires explicit locking.

Add a local_lock_t to the data structure and use
local_lock_nested_bh() for locking. This change adds only lockdep
coverage and does not alter the functional behaviour for !PREEMPT_RT.

Cc: Allison Henderson <allison.henderson@oracle.com>
Cc: linux-rdma@vger.kernel.org
Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-16-bigeasy@linutronix.de


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent 0af5928f

net/rds/page.c

+8 −2
Original line number Diff line number Diff line
@@ -40,10 +40,12 @@ 
struct rds_page_remainder {

	struct page	*r_page;

	unsigned long	r_offset;

	local_lock_t	bh_lock;

};



static

DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder, rds_page_remainders);

static DEFINE_PER_CPU_SHARED_ALIGNED(struct rds_page_remainder, rds_page_remainders) = {

	.bh_lock = INIT_LOCAL_LOCK(bh_lock),

};



/**

 * rds_page_remainder_alloc - build up regions of a message.
@@ -87,6 +89,7 @@ int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes, 
	}



	local_bh_disable();

	local_lock_nested_bh(&rds_page_remainders.bh_lock);

	rem = this_cpu_ptr(&rds_page_remainders);



	while (1) {
@@ -115,11 +118,13 @@ int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes, 
		}



		/* alloc if there is nothing for us to use */

		local_unlock_nested_bh(&rds_page_remainders.bh_lock);

		local_bh_enable();



		page = alloc_page(gfp);



		local_bh_disable();

		local_lock_nested_bh(&rds_page_remainders.bh_lock);

		rem = this_cpu_ptr(&rds_page_remainders);



		if (!page) {
@@ -138,6 +143,7 @@ int rds_page_remainder_alloc(struct scatterlist *scat, unsigned long bytes, 
		rem->r_offset = 0;

	}



	local_unlock_nested_bh(&rds_page_remainders.bh_lock);

	local_bh_enable();

out:

	rdsdebug("bytes %lu ret %d %p %u %u\n", bytes, ret,