0fa294fb1985 ("cgroup: Replace cgroup_rstat_mutex with a spinlock") added
cgroup_rstat_flush_irqsafe() allowing flushing to happen from the irq
context. However, rstat paths use u64_stats_sync to synchronize access to
64bit stat counters on 32bit machines. u64_stats_sync is implemented using
seq_lock and trying to read from an irq context can lead to A-A deadlock if
the irq happens to interrupt the stat update.
Fix it by using the irqsafe variants - u64_stats_update_begin_irqsave() and
u64_stats_update_end_irqrestore() - in the update paths. Note that none of
this matters on 64bit machines. All these are just for 32bit SMP setups.
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reported-by: Rik van Riel <riel@xxxxxxxxxxx>
---
block/blk-cgroup.c | 14 ++++++++------
kernel/cgroup/rstat.c | 19 +++++++++++--------
2 files changed, 19 insertions(+), 14 deletions(-)
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -790,6 +790,7 @@ static void blkcg_rstat_flush(struct cgr
struct blkcg_gq *parent = blkg->parent;
struct blkg_iostat_set *bisc = per_cpu_ptr(blkg->iostat_cpu, cpu);
struct blkg_iostat cur, delta;
+ unsigned long flags;
unsigned int seq;
/* fetch the current per-cpu values */
@@ -799,21 +800,21 @@ static void blkcg_rstat_flush(struct cgr
} while (u64_stats_fetch_retry(&bisc->sync, seq));
/* propagate percpu delta to global */
- u64_stats_update_begin(&blkg->iostat.sync);
+ flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
blkg_iostat_set(&delta, &cur);
blkg_iostat_sub(&delta, &bisc->last);
blkg_iostat_add(&blkg->iostat.cur, &delta);
blkg_iostat_add(&bisc->last, &delta);
- u64_stats_update_end(&blkg->iostat.sync);
+ u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
/* propagate global delta to parent (unless that's root) */
if (parent && parent->parent) {
- u64_stats_update_begin(&parent->iostat.sync);
+ flags = u64_stats_update_begin_irqsave(&parent->iostat.sync);
blkg_iostat_set(&delta, &blkg->iostat.cur);
blkg_iostat_sub(&delta, &blkg->iostat.last);
blkg_iostat_add(&parent->iostat.cur, &delta);
blkg_iostat_add(&blkg->iostat.last, &delta);
- u64_stats_update_end(&parent->iostat.sync);
+ u64_stats_update_end_irqrestore(&parent->iostat.sync, flags);
}
}
@@ -848,6 +849,7 @@ static void blkcg_fill_root_iostats(void
memset(&tmp, 0, sizeof(tmp));
for_each_possible_cpu(cpu) {
struct disk_stats *cpu_dkstats;
+ unsigned long flags;
cpu_dkstats = per_cpu_ptr(bdev->bd_stats, cpu);
tmp.ios[BLKG_IOSTAT_READ] +=
@@ -864,9 +866,9 @@ static void blkcg_fill_root_iostats(void
tmp.bytes[BLKG_IOSTAT_DISCARD] +=
cpu_dkstats->sectors[STAT_DISCARD] << 9;
- u64_stats_update_begin(&blkg->iostat.sync);
+ flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync);
blkg_iostat_set(&blkg->iostat.cur, &tmp);
- u64_stats_update_end(&blkg->iostat.sync);
+ u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags);
}
}
}
--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -347,19 +347,20 @@ static void cgroup_base_stat_flush(struc
}
static struct cgroup_rstat_cpu *
-cgroup_base_stat_cputime_account_begin(struct cgroup *cgrp)
+cgroup_base_stat_cputime_account_begin(struct cgroup *cgrp, unsigned long *flags)
{
struct cgroup_rstat_cpu *rstatc;
rstatc = get_cpu_ptr(cgrp->rstat_cpu);
- u64_stats_update_begin(&rstatc->bsync);
+ *flags = u64_stats_update_begin_irqsave(&rstatc->bsync);
return rstatc;
}
static void cgroup_base_stat_cputime_account_end(struct cgroup *cgrp,
- struct cgroup_rstat_cpu *rstatc)
+ struct cgroup_rstat_cpu *rstatc,
+ unsigned long flags)
{
- u64_stats_update_end(&rstatc->bsync);
+ u64_stats_update_end_irqrestore(&rstatc->bsync, flags);
cgroup_rstat_updated(cgrp, smp_processor_id());
put_cpu_ptr(rstatc);
}
@@ -367,18 +368,20 @@ static void cgroup_base_stat_cputime_acc
void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec)
{
struct cgroup_rstat_cpu *rstatc;
+ unsigned long flags;
- rstatc = cgroup_base_stat_cputime_account_begin(cgrp);
+ rstatc = cgroup_base_stat_cputime_account_begin(cgrp, &flags);
rstatc->bstat.cputime.sum_exec_runtime += delta_exec;
- cgroup_base_stat_cputime_account_end(cgrp, rstatc);
+ cgroup_base_stat_cputime_account_end(cgrp, rstatc, flags);
}
void __cgroup_account_cputime_field(struct cgroup *cgrp,
enum cpu_usage_stat index, u64 delta_exec)
{
struct cgroup_rstat_cpu *rstatc;
+ unsigned long flags;
- rstatc = cgroup_base_stat_cputime_account_begin(cgrp);
+ rstatc = cgroup_base_stat_cputime_account_begin(cgrp, &flags);
switch (index) {
case CPUTIME_USER:
@@ -394,7 +397,7 @@ void __cgroup_account_cputime_field(stru
break;
}
- cgroup_base_stat_cputime_account_end(cgrp, rstatc);
+ cgroup_base_stat_cputime_account_end(cgrp, rstatc, flags);
}
/*
