Bit spinlocks are problematic if PREEMPT_RT is enabled. They disable preemption, which is undesired for latency reasons and breaks when regular spinlocks are taken within the bit_spinlock locked region because regular spinlocks are converted to 'sleeping spinlocks' on RT.
Substitute the BH_State and BH_JournalHead bit spinlocks with regular spinlock for PREEMPT_RT enabled kernels. Bit spinlocks are also not covered by lock debugging, e.g. lockdep. With the spinlock substitution in place, they can be exposed via CONFIG_DEBUG_BIT_SPINLOCKS. Originally-by: Steven Rostedt <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Cc: [email protected] Cc: "Theodore Ts'o" <[email protected]> Cc: Matthew Wilcox <[email protected]> Cc: Jan Kara <[email protected]> -- include/linux/buffer_head.h | 8 ++++++++ include/linux/jbd2.h | 36 ++++++++++++++++++++++++++++++++++++ 2 files changed, 44 insertions(+) --- a/include/linux/buffer_head.h +++ b/include/linux/buffer_head.h @@ -79,6 +79,10 @@ struct buffer_head { #if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS) spinlock_t b_uptodate_lock; +# if IS_ENABLED(CONFIG_JBD2) + spinlock_t b_state_lock; + spinlock_t b_journal_head_lock; +# endif #endif }; @@ -101,6 +105,10 @@ bh_uptodate_unlock_irqrestore(struct buf static inline void buffer_head_init_locks(struct buffer_head *bh) { spin_lock_init(&bh->b_uptodate_lock); +#if IS_ENABLED(CONFIG_JBD2) + spin_lock_init(&bh->b_state_lock); + spin_lock_init(&bh->b_journal_head_lock); +#endif } #else /* PREEMPT_RT || DEBUG_BIT_SPINLOCKS */ --- a/include/linux/jbd2.h +++ b/include/linux/jbd2.h @@ -342,6 +342,40 @@ static inline struct journal_head *bh2jh return bh->b_private; } +#if defined(CONFIG_PREEMPT_RT) || defined(CONFIG_DEBUG_BIT_SPINLOCKS) + +static inline void jbd_lock_bh_state(struct buffer_head *bh) +{ + spin_lock(&bh->b_state_lock); +} + +static inline int jbd_trylock_bh_state(struct buffer_head *bh) +{ + return spin_trylock(&bh->b_state_lock); +} + +static inline int jbd_is_locked_bh_state(struct buffer_head *bh) +{ + return spin_is_locked(&bh->b_state_lock); +} + +static inline void jbd_unlock_bh_state(struct buffer_head *bh) +{ + spin_unlock(&bh->b_state_lock); +} + +static inline void jbd_lock_bh_journal_head(struct buffer_head *bh) +{ + spin_lock(&bh->b_journal_head_lock); +} + +static inline void jbd_unlock_bh_journal_head(struct buffer_head *bh) +{ + spin_unlock(&bh->b_journal_head_lock); +} + +#else /* PREEMPT_RT || DEBUG_BIT_SPINLOCKS */ + static inline void jbd_lock_bh_state(struct buffer_head *bh) { bit_spin_lock(BH_State, &bh->b_state); @@ -372,6 +406,8 @@ static inline void jbd_unlock_bh_journal bit_spin_unlock(BH_JournalHead, &bh->b_state); } +#endif /* !PREEMPT_RT && !DEBUG_BIT_SPINLOCKS */ + #define J_ASSERT(assert) BUG_ON(!(assert)) #define J_ASSERT_BH(bh, expr) J_ASSERT(expr)
