Commit 03a001b1 authored by Suren Baghdasaryan's avatar Suren Baghdasaryan Committed by Peter Zijlstra
Browse files

mm: introduce mmap_lock_speculate_{try_begin|retry} 



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: default avatarPeter Zijlstra <peterz@infradead.org>
Signed-off-by: default avatarSuren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarLiam R. Howlett <Liam.Howlett@Oracle.com>
Link: https://lkml.kernel.org/r/20241122174416.1367052-3-surenb@google.com
parent eb449bd9

include/linux/mmap_lock.h

+31 −2
Original line number Diff line number Diff line
@@ -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 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)

{