lkml.org 
[lkml]   [2021]   [Apr]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC PATCH 23/37] mm: rcu safe vma->vm_file freeing
Date
Defer freeing of vma->vm_file when freeing vmas.
This is to allow speculative page faults in the mapped file case.

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
---
fs/exec.c | 1 +
kernel/fork.c | 17 +++++++++++++++--
mm/mmap.c | 11 +++++++----
mm/nommu.c | 6 ++----
4 files changed, 25 insertions(+), 10 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index 18594f11c31f..c9da73eb0f53 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -286,6 +286,7 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
mmap_write_unlock(mm);
err_free:
bprm->vma = NULL;
+ VM_BUG_ON(vma->vm_file);
vm_area_free(vma);
return err;
}
diff --git a/kernel/fork.c b/kernel/fork.c
index b6078e546114..2f20a5c5fed8 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -369,19 +369,31 @@ struct vm_area_struct *vm_area_dup(struct vm_area_struct *orig)
return new;
}

+static inline void ____vm_area_free(struct vm_area_struct *vma)
+{
+ if (vma->vm_file)
+ fput(vma->vm_file);
+ kmem_cache_free(vm_area_cachep, vma);
+}
+
#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
static void __vm_area_free(struct rcu_head *head)
{
struct vm_area_struct *vma = container_of(head, struct vm_area_struct,
vm_rcu);
- kmem_cache_free(vm_area_cachep, vma);
+ ____vm_area_free(vma);
}

+#endif
+
void vm_area_free(struct vm_area_struct *vma)
{
+#ifdef CONFIG_SPECULATIVE_PAGE_FAULT
call_rcu(&vma->vm_rcu, __vm_area_free);
+#else
+ ____vm_area_free(vma);
+#endif
}
-#endif /* CONFIG_SPECULATIVE_PAGE_FAULT */

static void account_kernel_stack(struct task_struct *tsk, int account)
{
@@ -621,6 +633,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
fail_nomem_anon_vma_fork:
mpol_put(vma_policy(tmp));
fail_nomem_policy:
+ tmp->vm_file = NULL; /* prevents fput within vm_area_free() */
vm_area_free(tmp);
fail_nomem:
retval = -ENOMEM;
diff --git a/mm/mmap.c b/mm/mmap.c
index 3f287599a7a3..cc2323e243bb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -178,9 +178,8 @@ static struct vm_area_struct *remove_vma(struct vm_area_struct *vma)
might_sleep();
if (vma->vm_ops && vma->vm_ops->close)
vma->vm_ops->close(vma);
- if (vma->vm_file)
- fput(vma->vm_file);
mpol_put(vma_policy(vma));
+ /* fput(vma->vm_file) happens in vm_area_free after an RCU delay. */
vm_area_free(vma);
return next;
}
@@ -949,7 +948,8 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
if (remove_next) {
if (file) {
uprobe_munmap(next, next->vm_start, next->vm_end);
- fput(file);
+ /* fput(file) happens whthin vm_area_free(next) */
+ VM_BUG_ON(file != next->vm_file);
}
if (next->anon_vma)
anon_vma_merge(vma, next);
@@ -1828,7 +1828,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
* fput the vma->vm_file here or we would add an extra fput for file
* and cause general protection fault ultimately.
*/
- fput(vma->vm_file);
+ /* fput happens within vm_area_free */
vm_area_free(vma);
vma = merge;
/* Update vm_flags to pick up the change. */
@@ -1907,6 +1907,7 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
if (vm_flags & VM_DENYWRITE)
allow_write_access(file);
free_vma:
+ VM_BUG_ON(vma->vm_file);
vm_area_free(vma);
unacct_error:
if (charged)
@@ -2779,6 +2780,7 @@ int __split_vma(struct mm_struct *mm, struct vm_area_struct *vma,
out_free_mpol:
mpol_put(vma_policy(new));
out_free_vma:
+ new->vm_file = NULL; /* prevents fput within vm_area_free() */
vm_area_free(new);
return err;
}
@@ -3343,6 +3345,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
out_free_mempol:
mpol_put(vma_policy(new_vma));
out_free_vma:
+ new_vma->vm_file = NULL; /* Prevent fput within vm_area_free */
vm_area_free(new_vma);
out:
return NULL;
diff --git a/mm/nommu.c b/mm/nommu.c
index 5c9ab799c0e6..06a0dc0b913b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -664,9 +664,8 @@ static void delete_vma(struct mm_struct *mm, struct vm_area_struct *vma)
{
if (vma->vm_ops && vma->vm_ops->close)
vma->vm_ops->close(vma);
- if (vma->vm_file)
- fput(vma->vm_file);
put_nommu_region(vma->vm_region);
+ /* fput(vma->vm_file) happens within vm_area_free() */
vm_area_free(vma);
}

@@ -1267,8 +1266,7 @@ unsigned long do_mmap(struct file *file,
if (region->vm_file)
fput(region->vm_file);
kmem_cache_free(vm_region_jar, region);
- if (vma->vm_file)
- fput(vma->vm_file);
+ /* fput(vma->vm_file) happens within vm_area_free() */
vm_area_free(vma);
return ret;

--
2.20.1
\
 
 \ /
  Last update: 2021-04-07 03:52    [W:0.239 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site