[PATCH v3 0/3] aio: ctx->dead cleanups

[PATCH v3 0/3] aio: ctx->dead cleanups

[Oleg Nesterov]

As Jeff suggested, 1/3 was changed to simply remove the ->dead check.
I also updated the changelog.

Jeff, I preserved your acks in 2-3.

Oleg.

[PATCH v3 1/3] aio_ring_remap: kill the bogus ctx->dead check

[Oleg Nesterov]

kill_ioctx() sets ctx->dead and removes ctx from ->ioctx_table
"atomically" under mm->ioctx_lock, so aio_ring_remap() can never
see a dead ctx.

And even -EINVAL doesn't look necessary. Yes, if mremap() races
with kill_ioctx() vm_munmap(ctx->mmap_base, ctx->mmap_size) can
unmap the wrong region. In this case the buggy application should
blame itself. And there are other reasons why that vm_munmap() can
be wrong. Say, an application can mremap() the part of aio region
and then do io_destroy(). We could change aio_ring_remap() to
verify vma->that vma_end - vma->vma_start == ctx->mmap_size but
this won't help if the application does munmap() instead.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 fs/aio.c |    9 +++------
 1 files changed, 3 insertions(+), 6 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 480440f..893d300 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -325,14 +325,11 @@ static int aio_ring_remap(struct file *file, struct vm_area_struct *vma)
 	rcu_read_lock();
 	table = rcu_dereference(mm->ioctx_table);
 	for (i = 0; i < table->nr; i++) {
-		struct kioctx *ctx;
+		struct kioctx *ctx = table->table[i];
 
-		ctx = table->table[i];
 		if (ctx && ctx->aio_ring_file == file) {
-			if (!atomic_read(&ctx->dead)) {
-				ctx->user_id = ctx->mmap_base = vma->vm_start;
-				res = 0;
-			}
+			ctx->user_id = ctx->mmap_base = vma->vm_start;
+			res = 0;
 			break;
 		}
 	}
-- 
1.5.5.1

[PATCH v3 2/3] aio: make aio_ring->dead boolean

[Oleg Nesterov]

"atomic_t dead" makes no sense. atomic_read() is the plain LOAD,
it doesn't have some "additional" synchronization with xchg().

And now that kill_ioctx() sets "dead" under mm->ioctx_lock we do
not even need xchg().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
---
 fs/aio.c |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index 893d300..d63a889 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -84,7 +84,7 @@ struct ctx_rq_wait {
 
 struct kioctx {
 	struct percpu_ref	users;
-	atomic_t		dead;
+	bool			dead;
 
 	struct percpu_ref	reqs;
 
@@ -765,7 +765,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
 err_cleanup:
 	aio_nr_sub(ctx->max_reqs);
 err_ctx:
-	atomic_set(&ctx->dead, 1);
+	ctx->dead = true; /* unneeded */
 	if (ctx->mmap_size)
 		vm_munmap(ctx->mmap_base, ctx->mmap_size);
 	aio_free_ring(ctx);
@@ -790,11 +790,12 @@ static int kill_ioctx(struct mm_struct *mm, struct kioctx *ctx,
 	struct kioctx_table *table;
 
 	spin_lock(&mm->ioctx_lock);
-	if (atomic_xchg(&ctx->dead, 1)) {
+	if (unlikely(ctx->dead)) {
 		spin_unlock(&mm->ioctx_lock);
 		return -EINVAL;
 	}
 
+	ctx->dead = true;
 	table = rcu_dereference_raw(mm->ioctx_table);
 	WARN_ON(ctx != table->table[ctx->id]);
 	table->table[ctx->id] = NULL;
@@ -1236,7 +1237,7 @@ static bool aio_read_events(struct kioctx *ctx, long min_nr, long nr,
 	if (ret > 0)
 		*i += ret;
 
-	if (unlikely(atomic_read(&ctx->dead)))
+	if (unlikely(ctx->dead))
 		ret = -EINVAL;
 
 	if (!*i)
-- 
1.5.5.1

Re: [PATCH v3 2/3] aio: make aio_ring->dead boolean

[Jeff Moyer]

Oleg Nesterov <oleg@redhat.com> writes:

> "atomic_t dead" makes no sense. atomic_read() is the plain LOAD,
> it doesn't have some "additional" synchronization with xchg().
>
> And now that kill_ioctx() sets "dead" under mm->ioctx_lock we do
> not even need xchg().
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> Reviewed-by: Jeff Moyer <jmoyer@redhat.com>

> @@ -765,7 +765,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
>  err_cleanup:
>  	aio_nr_sub(ctx->max_reqs);
>  err_ctx:
> -	atomic_set(&ctx->dead, 1);
> +	ctx->dead = true; /* unneeded */

I was hoping you'd remove this line entirely.

-Jeff

Re: [PATCH v3 2/3] aio: make aio_ring->dead boolean

[Oleg Nesterov]

On 06/18, Jeff Moyer wrote:
>
> Oleg Nesterov <oleg@redhat.com> writes:
> > @@ -765,7 +765,7 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
> >  err_cleanup:
> >  	aio_nr_sub(ctx->max_reqs);
> >  err_ctx:
> > -	atomic_set(&ctx->dead, 1);
> > +	ctx->dead = true; /* unneeded */
>
> I was hoping you'd remove this line entirely.

Ah. I didn't understand you wamt me to do this... OK, please see v4.

Oleg.

[PATCH v3 3/3] aio_free_ring: don't do page_count(NULL)

[Oleg Nesterov]

aio_free_ring() can actually see the NULL page in ->ring_pages[],
this can happen if aio_setup_ring() fails.

And in this case page_count(ctx->ring_pages[i]) can OOPS.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
---
 fs/aio.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index d63a889..b9947ed 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -292,12 +292,12 @@ static void aio_free_ring(struct kioctx *ctx)
 	put_aio_ring_file(ctx);
 
 	for (i = 0; i < ctx->nr_pages; i++) {
-		struct page *page;
-		pr_debug("pid(%d) [%d] page->count=%d\n", current->pid, i,
-				page_count(ctx->ring_pages[i]));
-		page = ctx->ring_pages[i];
+		struct page *page = ctx->ring_pages[i];
 		if (!page)
 			continue;
+
+		pr_debug("pid(%d) [%d] page->count=%d\n",
+				current->pid, i, page_count(page));
 		ctx->ring_pages[i] = NULL;
 		put_page(page);
 	}
-- 
1.5.5.1