drivers/block/zram/zram_drv.c | 37 +++++++++++++++++++++++++++++++++++++ drivers/block/zram/zram_drv.h | 3 +++ 2 files changed, 40 insertions(+)
From: Mike Galbraith <umgwanakikbuti@gmail.com>
The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping
lock on PREEMPT_RT and it can not be acquired in this context. In this locked
section, zs_free() acquires a zs_pool::lock, and there is access to
zram::wb_limit_lock.
Use a spinlock_t on PREEMPT_RT for locking and set/ clear ZRAM_LOCK bit after
the lock has been acquired/ dropped.
Signed-off-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
I posted this few times. Mikes intents to keep it based on last feedback.
Any reason not to apply it?
https://lkml.kernel.org/r/YqIbMuHCPiQk+Ac2@linutronix.de
https://lore.kernel.org/20230323161830.jFbWCosd@linutronix.de
drivers/block/zram/zram_drv.c | 37 +++++++++++++++++++++++++++++++++++++
drivers/block/zram/zram_drv.h | 3 +++
2 files changed, 40 insertions(+)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -57,6 +57,41 @@ static void zram_free_page(struct zram *
static int zram_read_page(struct zram *zram, struct page *page, u32 index,
struct bio *parent);
+#ifdef CONFIG_PREEMPT_RT
+static void zram_meta_init_table_locks(struct zram *zram, size_t num_pages)
+{
+ size_t index;
+
+ for (index = 0; index < num_pages; index++)
+ spin_lock_init(&zram->table[index].lock);
+}
+
+static int zram_slot_trylock(struct zram *zram, u32 index)
+{
+ int ret;
+
+ ret = spin_trylock(&zram->table[index].lock);
+ if (ret)
+ __set_bit(ZRAM_LOCK, &zram->table[index].flags);
+ return ret;
+}
+
+static void zram_slot_lock(struct zram *zram, u32 index)
+{
+ spin_lock(&zram->table[index].lock);
+ __set_bit(ZRAM_LOCK, &zram->table[index].flags);
+}
+
+static void zram_slot_unlock(struct zram *zram, u32 index)
+{
+ __clear_bit(ZRAM_LOCK, &zram->table[index].flags);
+ spin_unlock(&zram->table[index].lock);
+}
+
+#else
+
+static void zram_meta_init_table_locks(struct zram *zram, size_t num_pages) { }
+
static int zram_slot_trylock(struct zram *zram, u32 index)
{
return bit_spin_trylock(ZRAM_LOCK, &zram->table[index].flags);
@@ -71,6 +106,7 @@ static void zram_slot_unlock(struct zram
{
bit_spin_unlock(ZRAM_LOCK, &zram->table[index].flags);
}
+#endif
static inline bool init_done(struct zram *zram)
{
@@ -1226,6 +1262,7 @@ static bool zram_meta_alloc(struct zram
if (!huge_class_size)
huge_class_size = zs_huge_class_size(zram->mem_pool);
+ zram_meta_init_table_locks(zram, num_pages);
return true;
}
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -69,6 +69,9 @@ struct zram_table_entry {
unsigned long element;
};
unsigned long flags;
+#ifdef CONFIG_PREEMPT_RT
+ spinlock_t lock;
+#endif
#ifdef CONFIG_ZRAM_TRACK_ENTRY_ACTIME
ktime_t ac_time;
#endifOn 6/19/24 9:08 AM, Sebastian Andrzej Siewior wrote: > From: Mike Galbraith <umgwanakikbuti@gmail.com> > > The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping > lock on PREEMPT_RT and it can not be acquired in this context. In this locked > section, zs_free() acquires a zs_pool::lock, and there is access to > zram::wb_limit_lock. > > Use a spinlock_t on PREEMPT_RT for locking and set/ clear ZRAM_LOCK bit after > the lock has been acquired/ dropped. The conditional code depending on CONFIG_PREEMPT_RT is nasty. Why not just get rid of that and use the CONFIG_PREEMPT_RT variants for everything? They are either good enough to work well in general, or it should be redone such that it is. -- Jens Axboe
On 2024-06-19 11:34:23 [-0600], Jens Axboe wrote: > On 6/19/24 9:08 AM, Sebastian Andrzej Siewior wrote: > > From: Mike Galbraith <umgwanakikbuti@gmail.com> > > > > The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping > > lock on PREEMPT_RT and it can not be acquired in this context. In this locked > > section, zs_free() acquires a zs_pool::lock, and there is access to > > zram::wb_limit_lock. > > > > Use a spinlock_t on PREEMPT_RT for locking and set/ clear ZRAM_LOCK bit after > > the lock has been acquired/ dropped. > > The conditional code depending on CONFIG_PREEMPT_RT is nasty. Why not > just get rid of that and use the CONFIG_PREEMPT_RT variants for > everything? They are either good enough to work well in general, or it > should be redone such that it is. That would increase the struct size with lockdep for !RT. But it is probably not a concern. Also other bits (besides ZRAM_LOCK) can not be added but that wasn't needed in the last few years. Okay, let me redo it. Sebastian
On 6/19/24 11:52 AM, Sebastian Andrzej Siewior wrote: > On 2024-06-19 11:34:23 [-0600], Jens Axboe wrote: >> On 6/19/24 9:08 AM, Sebastian Andrzej Siewior wrote: >>> From: Mike Galbraith <umgwanakikbuti@gmail.com> >>> >>> The bit spinlock disables preemption. The spinlock_t lock becomes a sleeping >>> lock on PREEMPT_RT and it can not be acquired in this context. In this locked >>> section, zs_free() acquires a zs_pool::lock, and there is access to >>> zram::wb_limit_lock. >>> >>> Use a spinlock_t on PREEMPT_RT for locking and set/ clear ZRAM_LOCK bit after >>> the lock has been acquired/ dropped. >> >> The conditional code depending on CONFIG_PREEMPT_RT is nasty. Why not >> just get rid of that and use the CONFIG_PREEMPT_RT variants for >> everything? They are either good enough to work well in general, or it >> should be redone such that it is. > > That would increase the struct size with lockdep for !RT. But it is > probably not a concern. Also other bits (besides ZRAM_LOCK) can not be > added but that wasn't needed in the last few years. Yeah I really don't think anyone cares about the struct size when PROVE_LOCKING is on... -- Jens Axboe
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