[RFC PATCH] fs: proc: task_mmu: fix sparse warnings

[RFC PATCH] fs: proc: task_mmu: fix sparse warnings

[Anders Roxell]

When building the kernel with sparse enabled 'C=1' the following
warnings can be seen:

fs/proc/task_mmu.c:587:17: warning: context imbalance in 'smaps_pte_range' - unexpected unlock
fs/proc/task_mmu.c:1145:28: warning: context imbalance in 'clear_refs_pte_range' - unexpected unlock
fs/proc/task_mmu.c:1473:28: warning: context imbalance in 'pagemap_pmd_range' - unexpected unlock
fs/proc/task_mmu.c:1811:28: warning: context imbalance in 'gather_pte_stats' - unexpected unlock

Rework to add __acquire() and __release() to tell sparse that it is all good.

Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
---
 fs/proc/task_mmu.c | 31 +++++++++++++++++++++++++++++++
 mm/huge_memory.c   |  4 +++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ad667dbc96f5..6b702c030802 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -584,6 +584,13 @@ static int smaps_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (ptl) {
+		/*
+		 * Fake out sparse.
+		 * The pmd_lock are held in pmd_trans_huge_lock() and if we
+		 * get in here we have to unlock. We tell sparse that
+		 * everyting is as it should with the __acquire() directive.
+		 */
+		__acquire(ptl);
 		smaps_pmd_entry(pmd, addr, walk);
 		spin_unlock(ptl);
 		goto out;
@@ -1127,6 +1134,14 @@ static int clear_refs_pte_range(pmd_t *pmd, unsigned long addr,
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (ptl) {
+		/*
+		 * Fake out sparse.
+		 * The pmd_lock are held in pmd_trans_huge_lock() and if we
+		 * get in here we have to unlock. We tell sparse that
+		 * everyting is as it should with the __acquire() directive.
+		 */
+		__acquire(ptl);
+
 		if (cp->type == CLEAR_REFS_SOFT_DIRTY) {
 			clear_soft_dirty_pmd(vma, addr, pmd);
 			goto out;
@@ -1418,6 +1433,14 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 		pmd_t pmd = *pmdp;
 		struct page *page = NULL;
 
+		/*
+		 * Fake out sparse.
+		 * The pmd_lock are held in pmd_trans_huge_lock() and if we
+		 * get in here we have to unlock. We tell sparse that
+		 * everyting is as it should with the __acquire() directive.
+		 */
+		__acquire(ptl);
+
 		if (vma->vm_flags & VM_SOFTDIRTY)
 			flags |= PM_SOFT_DIRTY;
 
@@ -1804,6 +1827,14 @@ static int gather_pte_stats(pmd_t *pmd, unsigned long addr,
 	if (ptl) {
 		struct page *page;
 
+		/*
+		 * Fake out sparse.
+		 * The pmd_lock are held in pmd_trans_huge_lock() and if we
+		 * get in here we have to unlock. We tell sparse that
+		 * everyting is as it should with the __acquire() directive.
+		 */
+		__acquire(ptl);
+
 		page = can_gather_numa_stats_pmd(*pmd, vma, addr);
 		if (page)
 			gather_stats(page, md, pmd_dirty(*pmd),
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e5ea5f775d5c..c873bf5947ae 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1833,8 +1833,10 @@ spinlock_t *__pmd_trans_huge_lock(pmd_t *pmd, struct vm_area_struct *vma)
 	spinlock_t *ptl;
 	ptl = pmd_lock(vma->vm_mm, pmd);
 	if (likely(is_swap_pmd(*pmd) || pmd_trans_huge(*pmd) ||
-			pmd_devmap(*pmd)))
+			pmd_devmap(*pmd))) {
+		__release(ptl); /* fake out sparse */
 		return ptl;
+	}
 	spin_unlock(ptl);
 	return NULL;
 }
-- 
2.33.0

Re: [RFC PATCH] fs: proc: task_mmu: fix sparse warnings

[Matthew Wilcox]

On Thu, Oct 07, 2021 at 09:16:36PM +0200, Anders Roxell wrote:
> When building the kernel with sparse enabled 'C=1' the following
> warnings can be seen:
> 
> fs/proc/task_mmu.c:587:17: warning: context imbalance in 'smaps_pte_range' - unexpected unlock
> fs/proc/task_mmu.c:1145:28: warning: context imbalance in 'clear_refs_pte_range' - unexpected unlock
> fs/proc/task_mmu.c:1473:28: warning: context imbalance in 'pagemap_pmd_range' - unexpected unlock
> fs/proc/task_mmu.c:1811:28: warning: context imbalance in 'gather_pte_stats' - unexpected unlock
> 
> Rework to add __acquire() and __release() to tell sparse that it is all good.

Surely the root problem here is that pmd_trans_huge_lock() isn't
marked with __cond_lock() like, eg, get_locked_pte() is?