On 8/10/18 2:51 AM, Vlastimil Babka wrote:

On 08/10/2018 01:36 AM, Yang Shi wrote:

quoted

Unmapping vmas, which have VM_HUGETLB | VM_PFNMAP flag set or
have uprobes set, need get done with write mmap_sem held since
they may update vm_flags.

So, it might be not safe enough to deal with these kind of special
mappings with read mmap_sem. Deal with such mappings with regular
do_munmap() call.

Michal suggested to make this as a separate patch for safer and more
bisectable sake.

Hm I believe Michal meant the opposite "evolution" though. Patch 2/4
should be done in a way that special mappings keep using the regular
path, and this patch would convert them to the new path. Possibly even
each special case separately.

Aha, thanks. I understood it oppositely.

Yang

quoted

Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Yang Shi <redacted>
---
  mm/mmap.c | 24 ++++++++++++++++++++++++
  1 file changed, 24 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 2234d5a..06cb83c 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c

@@ -2766,6 +2766,16 @@ static inline void munlock_vmas(struct vm_area_struct *vma,
  	}
  }
  
+static inline bool can_zap_with_rlock(struct vm_area_struct *vma)
+{
+	if ((vma->vm_file &&
+	     vma_has_uprobes(vma, vma->vm_start, vma->vm_end)) ||
+	     (vma->vm_flags | (VM_HUGETLB | VM_PFNMAP)))
+		return false;
+
+	return true;
+}
+
  /*
   * Zap pages with read mmap_sem held
   *

@@ -2808,6 +2818,17 @@ static int do_munmap_zap_rlock(struct mm_struct *mm, unsigned long start,
  			goto out;
  	}
  
+	/*
+	 * Unmapping vmas, which have VM_HUGETLB | VM_PFNMAP flag set or
+	 * have uprobes set, need get done with write mmap_sem held since
+	 * they may update vm_flags. Deal with such mappings with regular
+	 * do_munmap() call.
+	 */
+	for (vma = start_vma; vma && vma->vm_start < end; vma = vma->vm_next) {
+		if (!can_zap_with_rlock(vma))
+			goto regular_path;
+	}
+
  	/* Handle mlocked vmas */
  	if (mm->locked_vm) {
  		vma = start_vma;

@@ -2828,6 +2849,9 @@ static int do_munmap_zap_rlock(struct mm_struct *mm, unsigned long start,
  
  	return 0;
  
+regular_path:
+	ret = do_munmap(mm, start, len, uf);
+
  out:
  	up_write(&mm->mmap_sem);
  	return ret;