| Message ID | 20200520052908.204642-8-walken@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add a new mmap locking API wrapping mmap_sem calls | expand |
On Tue, 19 May 2020, Michel Lespinasse wrote: >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> >Reviewed-by: Daniel Jordan <daniel.m.jordan@oracle.com> >Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Sigh, bpf, but ok. Reviewed-by: Davidlohr Bueso <dbueso@suse.de> >--- > include/linux/mmap_lock.h | 14 ++++++++++++++ > kernel/bpf/stackmap.c | 17 +++++------------ > 2 files changed, 19 insertions(+), 12 deletions(-) > >diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h >index a757cb30ae77..d1826ce42f00 100644 >--- a/include/linux/mmap_lock.h >+++ b/include/linux/mmap_lock.h >@@ -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 */ >diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c >index 11d41f0c7005..998968659892 100644 >--- a/kernel/bpf/stackmap.c >+++ b/kernel/bpf/stackmap.c >@@ -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 = ¤t->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(¤t->mm->mmap_sem.dep_map, _RET_IP_); > } > } > >-- >2.26.2.761.g0e0b3e54be-goog >
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h index a757cb30ae77..d1826ce42f00 100644 --- a/include/linux/mmap_lock.h +++ b/include/linux/mmap_lock.h @@ -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 */ diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 11d41f0c7005..998968659892 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -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 = ¤t->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(¤t->mm->mmap_sem.dep_map, _RET_IP_); } }