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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: Michel Lespinasse <walken@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Davidlohr 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: Linus Torvalds <torvalds@linux-foundation.org>
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@ -56,4 +56,18 @@ static inline void mmap_read_unlock(struct mm_struct *mm)
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up_read(&mm->mmap_sem);
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}
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static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm)
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{
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if (down_read_trylock(&mm->mmap_sem)) {
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rwsem_release(&mm->mmap_sem.dep_map, _RET_IP_);
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return true;
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}
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return false;
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}
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static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
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{
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up_read_non_owner(&mm->mmap_sem);
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}
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#endif /* _LINUX_MMAP_LOCK_H */
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@ -33,7 +33,7 @@ struct bpf_stack_map {
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/* irq_work to run up_read() for build_id lookup in nmi context */
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struct stack_map_irq_work {
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struct irq_work irq_work;
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struct rw_semaphore *sem;
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struct mm_struct *mm;
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};
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static void do_up_read(struct irq_work *entry)
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@ -44,8 +44,7 @@ static void do_up_read(struct irq_work *entry)
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return;
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work = container_of(entry, struct stack_map_irq_work, irq_work);
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up_read_non_owner(work->sem);
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work->sem = NULL;
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mmap_read_unlock_non_owner(work->mm);
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}
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static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
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@ -317,7 +316,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
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* with build_id.
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*/
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if (!user || !current || !current->mm || irq_work_busy ||
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mmap_read_trylock(current->mm) == 0) {
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!mmap_read_trylock_non_owner(current->mm)) {
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/* cannot access current->mm, fall back to ips */
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for (i = 0; i < trace_nr; i++) {
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id_offs[i].status = BPF_STACK_BUILD_ID_IP;
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@ -342,16 +341,10 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
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}
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if (!work) {
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mmap_read_unlock(current->mm);
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mmap_read_unlock_non_owner(current->mm);
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} else {
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work->sem = ¤t->mm->mmap_sem;
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work->mm = current->mm;
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irq_work_queue(&work->irq_work);
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/*
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* The irq_work will release the mmap_sem with
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* up_read_non_owner(). The rwsem_release() is called
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* here to release the lock from lockdep's perspective.
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*/
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rwsem_release(¤t->mm->mmap_sem.dep_map, _RET_IP_);
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}
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}
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