The new SRCU_READ_FLAVOR_ATOMIC prohibits sleeping in both readers and grace-period waits in order to permit waiting on an SRCU grace period within an OOM notifier. This means that srcu_advance_state() cannot acquire ->srcu_gp_mutex in this case, because mutex_lock() can sleep.
This commit therefore adds an is_atomic parameter to srcu_advance_state(). When this parameter is false, current behavior is maintained, in other words, ->srcu_gp_mutex is acquired and released as before. But when this is_atomic parameter is false, the caller is responsible for excluding other callers. Signed-off-by: Paul E. McKenney <[email protected]> --- kernel/rcu/srcutree.c | 23 +++++++++++++++-------- 1 file changed, 15 insertions(+), 8 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index d32c374ee72a..dc063eb49b0d 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -1941,13 +1941,16 @@ EXPORT_SYMBOL_GPL(srcu_batches_completed); /* * Core SRCU state machine. Push state bits of ->srcu_gp_seq * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has - * completed in that state. + * completed in that state. Set is_atomic to indicate that + * the caller is excluding other calls so that ->srcu_gp_mutex + * is not needed, and to indicate that blocking is forbidden. */ -static void srcu_advance_state(struct srcu_struct *ssp) +static void srcu_advance_state(struct srcu_struct *ssp, bool is_atomic) { int idx; - mutex_lock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_lock(&ssp->srcu_sup->srcu_gp_mutex); /* * Because readers might be delayed for an extended period after @@ -1965,7 +1968,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) { WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq)); raw_spin_unlock_irq_rcu_node(ssp->srcu_sup); - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; } idx = rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)); @@ -1973,7 +1977,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) srcu_gp_start(ssp); raw_spin_unlock_irq_rcu_node(ssp->srcu_sup); if (idx != SRCU_STATE_IDLE) { - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* Someone else started the grace period. */ } } @@ -1981,7 +1986,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) { idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]); if (!try_check_zero(ssp, idx, 1)) { - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* readers present, retry later. */ } srcu_flip(ssp); @@ -1999,7 +2005,8 @@ static void srcu_advance_state(struct srcu_struct *ssp) */ idx = !(ssp->srcu_ctrp - &ssp->sda->srcu_ctrs[0]); if (!try_check_zero(ssp, idx, 2)) { - mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); + if (!is_atomic) + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* readers present, retry later. */ } ssp->srcu_sup->srcu_n_exp_nodelay = 0; @@ -2107,7 +2114,7 @@ static void process_srcu(struct work_struct *work) sup = container_of(work, struct srcu_usage, work.work); ssp = sup->srcu_ssp; - srcu_advance_state(ssp); + srcu_advance_state(ssp, false); raw_spin_lock_irq_rcu_node(ssp->srcu_sup); curdelay = srcu_get_delay(ssp); raw_spin_unlock_irq_rcu_node(ssp->srcu_sup); -- 2.40.1
