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srcutree: Suppress srcu_advance_state() mutex_lock in atomic

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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 <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2026-08-18 10:51:42 -07:00
parent 835a10eeb0
commit 21345a8eff
1 changed files with 15 additions and 8 deletions
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23
kernel/rcu/srcutree.c
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@ -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);