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rds: Use nested-BH locking for rds_page_remainder

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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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20250512092736.229935-16-bigeasy@linutronix.de
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Sebastian Andrzej Siewior 2025-05-12 11:27:36 +02:00 committed by Paolo Abeni
parent 0af5928f35
commit c50d295c37
1 changed files with 8 additions and 2 deletions
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10
net/rds/page.c
View File

@ -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,