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    Subject[PATCH 5.2 098/413] rcu: Force inlining of rcu_read_lock()
    Date
    [ Upstream commit 6da9f775175e516fc7229ceaa9b54f8f56aa7924 ]

    When debugging options are turned on, the rcu_read_lock() function
    might not be inlined. This results in lockdep's print_lock() function
    printing "rcu_read_lock+0x0/0x70" instead of rcu_read_lock()'s caller.
    For example:

    [ 10.579995] =============================
    [ 10.584033] WARNING: suspicious RCU usage
    [ 10.588074] 4.18.0.memcg_v2+ #1 Not tainted
    [ 10.593162] -----------------------------
    [ 10.597203] include/linux/rcupdate.h:281 Illegal context switch in
    RCU read-side critical section!
    [ 10.606220]
    [ 10.606220] other info that might help us debug this:
    [ 10.606220]
    [ 10.614280]
    [ 10.614280] rcu_scheduler_active = 2, debug_locks = 1
    [ 10.620853] 3 locks held by systemd/1:
    [ 10.624632] #0: (____ptrval____) (&type->i_mutex_dir_key#5){.+.+}, at: lookup_slow+0x42/0x70
    [ 10.633232] #1: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70
    [ 10.640954] #2: (____ptrval____) (rcu_read_lock){....}, at: rcu_read_lock+0x0/0x70

    These "rcu_read_lock+0x0/0x70" strings are not providing any useful
    information. This commit therefore forces inlining of the rcu_read_lock()
    function so that rcu_read_lock()'s caller is instead shown.

    Signed-off-by: Waiman Long <longman@redhat.com>
    Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    include/linux/rcupdate.h | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index b25d20822e75..3508f4508a11 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -586,7 +586,7 @@ static inline void rcu_preempt_sleep_check(void) { }
    * read-side critical sections may be preempted and they may also block, but
    * only when acquiring spinlocks that are subject to priority inheritance.
    */
    -static inline void rcu_read_lock(void)
    +static __always_inline void rcu_read_lock(void)
    {
    __rcu_read_lock();
    __acquire(RCU);
    --
    2.20.1


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