Add helper functions to speculatively perform operations without read-locking mmap_lock, expecting that mmap_lock will not be write-locked and mm is not modified from under us. Suggested-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> --- Changes since v2 [1] - Added SOB, per Liam Howlett [1] https://lore.kernel.org/all/20241121162826.987947-3-surenb@xxxxxxxxxx/ include/linux/mmap_lock.h | 33 +++++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-) diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index 9715326f5a85..8ac3041df053 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -71,6 +71,7 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm) } #ifdef CONFIG_PER_VMA_LOCK + static inline void mm_lock_seqcount_init(struct mm_struct *mm) { seqcount_init(&mm->mm_lock_seq); @@ -87,11 +88,39 @@ static inline void mm_lock_seqcount_end(struct mm_struct *mm) do_raw_write_seqcount_end(&mm->mm_lock_seq); } -#else +static inline bool mmap_lock_speculate_try_begin(struct mm_struct *mm, unsigned int *seq) +{ + /* + * Since mmap_lock is a sleeping lock, and waiting for it to become + * unlocked is more or less equivalent with taking it ourselves, don't + * bother with the speculative path if mmap_lock is already write-locked + * and take the slow path, which takes the lock. + */ + return raw_seqcount_try_begin(&mm->mm_lock_seq, *seq); +} + +static inline bool mmap_lock_speculate_retry(struct mm_struct *mm, unsigned int seq) +{ + return do_read_seqcount_retry(&mm->mm_lock_seq, seq); +} + +#else /* CONFIG_PER_VMA_LOCK */ + static inline void mm_lock_seqcount_init(struct mm_struct *mm) {} static inline void mm_lock_seqcount_begin(struct mm_struct *mm) {} static inline void mm_lock_seqcount_end(struct mm_struct *mm) {} -#endif + +static inline bool mmap_lock_speculate_try_begin(struct mm_struct *mm, unsigned int *seq) +{ + return false; +} + +static inline bool mmap_lock_speculate_retry(struct mm_struct *mm, unsigned int seq) +{ + return true; +} + +#endif /* CONFIG_PER_VMA_LOCK */ static inline void mmap_init_lock(struct mm_struct *mm) { -- 2.47.0.371.ga323438b13-goog
