The patch titled
Subject: mmap locking API: add mmap_read_trylock_non_owner()
has been added to the -mm tree. Its filename is
mmap-locking-api-add-mmap_read_trylock_non_owner.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mmap-locking-api-add-mmap_read_trylock_non_owner.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mmap-locking-api-add-mmap_read_trylock_non_owner.patch
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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next and is updated
there every 3-4 working days
------------------------------------------------------
From: Michel Lespinasse <walken@xxxxxxxxxx>
Subject: 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.
Link: http://lkml.kernel.org/r/20200520052908.204642-8-walken@xxxxxxxxxx
Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Davidlohr Bueso <dbueso@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Cc: Jerome Glisse <jglisse@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Laurent Dufour <ldufour@xxxxxxxxxxxxx>
Cc: Liam Howlett <Liam.Howlett@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Ying Han <yinghan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mmap_lock.h | 14 ++++++++++++++
kernel/bpf/stackmap.c | 17 +++++------------
2 files changed, 19 insertions(+), 12 deletions(-)
--- a/include/linux/mmap_lock.h~mmap-locking-api-add-mmap_read_trylock_non_owner
+++ a/include/linux/mmap_lock.h
@@ -56,4 +56,18 @@ static inline void mmap_read_unlock(stru
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 */
--- a/kernel/bpf/stackmap.c~mmap-locking-api-add-mmap_read_trylock_non_owner
+++ a/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 *
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_offse
* 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_offse
}
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_);
}
}
_
Patches currently in -mm which might be from walken@xxxxxxxxxx are
mmap-locking-api-initial-implementation-as-rwsem-wrappers.patch
mmu-notifier-use-the-new-mmap-locking-api.patch
dma-reservations-use-the-new-mmap-locking-api.patch
mmap-locking-api-use-coccinelle-to-convert-mmap_sem-rwsem-call-sites.patch
mmap-locking-api-convert-mmap_sem-call-sites-missed-by-coccinelle.patch
mmap-locking-api-convert-nested-write-lock-sites.patch
mmap-locking-api-add-mmap_read_trylock_non_owner.patch
mmap-locking-api-add-mmap_lock_initializer.patch
mmap-locking-api-add-mmap_assert_locked-and-mmap_assert_write_locked.patch
mmap-locking-api-rename-mmap_sem-to-mmap_lock.patch
mmap-locking-api-convert-mmap_sem-api-comments.patch
mmap-locking-api-convert-mmap_sem-comments.patch
