The following commit has been merged into the core/rcu branch of tip: Commit-ID: 8c9e0cb32315835825ea1ad725a858a2d2ce4a8e Gitweb: https://git.kernel.org/tip/8c9e0cb32315835825ea1ad725a858a2d2ce4a8e Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Sun, 22 Dec 2019 19:36:33 -08:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Thu, 20 Feb 2020 16:01:11 -08:00 srcu: Fix __call_srcu()/srcu_get_delay() datarace The srcu_struct structure's ->srcu_gp_seq_needed_exp field is accessed locklessly, so updates must use WRITE_ONCE(). This commit therefore adds the needed WRITE_ONCE() invocations. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/srcutree.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index b1edac9..79848f7 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -534,7 +534,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) rcu_seq_end(&ssp->srcu_gp_seq); gpseq = rcu_seq_current(&ssp->srcu_gp_seq); if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq)) - ssp->srcu_gp_seq_needed_exp = gpseq; + WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq); spin_unlock_irq_rcu_node(ssp); mutex_unlock(&ssp->srcu_gp_mutex); /* A new grace period can start at this point. But only one. */ @@ -614,7 +614,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp } spin_lock_irqsave_rcu_node(ssp, flags); if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) - ssp->srcu_gp_seq_needed_exp = s; + WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); spin_unlock_irqrestore_rcu_node(ssp, flags); } @@ -674,7 +674,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/ } if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) - ssp->srcu_gp_seq_needed_exp = s; + WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); /* If grace period not already done and none in progress, start it. */ if (!rcu_seq_done(&ssp->srcu_gp_seq, s) &&
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