Commit 0cc55a02 authored by Michel Lespinasse's avatar Michel Lespinasse Committed by Linus Torvalds
Browse files

mmap locking API: add mmap_read_trylock_non_owner() 



Add a couple APIs used by kernel/bpf/stackmap.c only:
- mmap_read_trylock_non_owner()
- mmap_read_unlock_non_owner() (may be called from a work queue).

It's still not ideal that bpf/stackmap subverts the lock ownership in this
way.  Thanks to Peter Zijlstra for suggesting this API as the least-ugly
way of addressing this in the short term.

Signed-off-by: default avatarMichel Lespinasse <walken@google.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarDaniel Jordan <daniel.m.jordan@oracle.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarDavidlohr Bueso <dbueso@suse.de>
Cc: David Rientjes <rientjes@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jerome Glisse <jglisse@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ying Han <yinghan@google.com>
Link: http://lkml.kernel.org/r/20200520052908.204642-8-walken@google.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent aaa2cc56

include/linux/mmap_lock.h

+14 −0
Original line number Diff line number Diff line
@@ -56,4 +56,18 @@ static inline void mmap_read_unlock(struct mm_struct *mm) 
	up_read(&mm->mmap_sem);

}



static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm)

{

	if (down_read_trylock(&mm->mmap_sem)) {

		rwsem_release(&mm->mmap_sem.dep_map, _RET_IP_);

		return true;

	}

	return false;

}



static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)

{

	up_read_non_owner(&mm->mmap_sem);

}



#endif /* _LINUX_MMAP_LOCK_H */

kernel/bpf/stackmap.c

+5 −12
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ struct bpf_stack_map { 
/* irq_work to run up_read() for build_id lookup in nmi context */

struct stack_map_irq_work {

	struct irq_work irq_work;

	struct rw_semaphore *sem;

	struct mm_struct *mm;

};



static void do_up_read(struct irq_work *entry)
@@ -44,8 +44,7 @@ static void do_up_read(struct irq_work *entry) 
		return;



	work = container_of(entry, struct stack_map_irq_work, irq_work);

	up_read_non_owner(work->sem);

	work->sem = NULL;

	mmap_read_unlock_non_owner(work->mm);

}



static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
@@ -317,7 +316,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, 
	 * with build_id.

	 */

	if (!user || !current || !current->mm || irq_work_busy ||

	    mmap_read_trylock(current->mm) == 0) {

	    !mmap_read_trylock_non_owner(current->mm)) {

		/* cannot access current->mm, fall back to ips */

		for (i = 0; i < trace_nr; i++) {

			id_offs[i].status = BPF_STACK_BUILD_ID_IP;
@@ -342,16 +341,10 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, 
	}



	if (!work) {

		mmap_read_unlock(current->mm);

		mmap_read_unlock_non_owner(current->mm);

	} else {

		work->sem = &current->mm->mmap_sem;

		work->mm = current->mm;

		irq_work_queue(&work->irq_work);

		/*

		 * The irq_work will release the mmap_sem with

		 * up_read_non_owner(). The rwsem_release() is called

		 * here to release the lock from lockdep's perspective.

		 */

		rwsem_release(&current->mm->mmap_sem.dep_map, _RET_IP_);

	}

}

CRA Git | Maintained and supported by SUSTech CRA and CCSE