[PATCH v3 06/10] mmap locking API: convert nested write lock sites

Michel Lespinasse
2020-03-27T22:51:27Z

Add API for nested write locks and convert the few call sites doing that.

Signed-off-by: Michel Lespinasse <walken@google.com>
---
arch/um/include/asm/mmu_context.h | 5 +++--
include/linux/mmap_lock.h | 11 +++++++++++
kernel/fork.c | 4 ++--
3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
index 62262c5c7785..cc15173f7518 100644
--- a/arch/um/include/asm/mmu_context.h
+++ b/arch/um/include/asm/mmu_context.h
@@ -8,6 +8,7 @@

#include <linux/sched.h>
#include <linux/mm_types.h>
+#include <linux/mmap_lock.h>

#include <asm/mmu.h>

@@ -47,9 +48,9 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new)
* when the new ->mm is used for the first time.
*/
__switch_mm(&new->context.id);
- down_write_nested(&new->mmap_sem, 1);
+ mmap_write_lock_nested(new, 1);
uml_setup_stubs(new);
- mmap_write_unlock(new);
+ mmap_write_unlock_nested(new);
}

static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 8b5a3cd56118..36fb758401d6 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h
@@ -11,6 +11,11 @@ static inline void mmap_write_lock(struct mm_struct *mm)
down_write(&mm->mmap_sem);
}

+static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass)
+{
+ down_write_nested(&mm->mmap_sem, subclass);
+}
+
static inline int mmap_write_lock_killable(struct mm_struct *mm)
{
return down_write_killable(&mm->mmap_sem);
@@ -26,6 +31,12 @@ static inline void mmap_write_unlock(struct mm_struct *mm)
up_write(&mm->mmap_sem);
}

+/* Pairs with mmap_write_lock_nested() */
+static inline void mmap_write_unlock_nested(struct mm_struct *mm)
+{
+ up_write(&mm->mmap_sem);
+}
+
static inline void mmap_downgrade_write_lock(struct mm_struct *mm)
{
downgrade_write(&mm->mmap_sem);
diff --git a/kernel/fork.c b/kernel/fork.c
index c321910d46e8..3460308b2213 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -497,7 +497,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
/*
* Not linked in yet - no deadlock potential:
*/
- down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
+ mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING);

/* No ordering required: file already has been exposed. */
RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
@@ -612,7 +612,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
/* a new mm has just been created */
retval = arch_dup_mmap(oldmm, mm);
out:
- mmap_write_unlock(mm);
+ mmap_write_unlock_nested(mm);
flush_tlb_mm(oldmm);
mmap_write_unlock(oldmm);
dup_userfaultfd_complete(&uf);
--
2.26.0.rc2.310.g2932bb562d-goog