On Mon, Aug 05, 2013 at 12:08:28PM -0400, Benjamin LaHaise wrote:
> Hi Sasha,
>
> On Mon, Aug 05, 2013 at 09:57:08AM -0400, Sasha Levin wrote:
> > Hi all,
> >
> > While fuzzing with trinity inside a KVM tools guest running latest -next
> > kernel,
> > I've stumbled on the following spew caused by a new BUG() added in "aio: fix
> > io_destroy() regression by using call_rcu()".
>
> I did some investigating, and it looks like there is a problem with
> db446a08c23d5475e6b08c87acca79ebb20f283c (aio: convert the ioctx list to
> table lookup v3). Can you confirm if reverting this patch eliminates
> the BUG() you're hitting? In my testing, I wasn't able to trigger the
> BUG(), but I was able to trip up slab corruption with debugging on.
And here is a patch that should fix the problems introduced in the table
lookup patch without reverting. I will add this to the aio-next.git tree.
This bug is not present in Linus' tree.
-ben
aio.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 588aff9..3bc068c 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -475,7 +475,7 @@ static int ioctx_add_table(struct kioctx *ctx, struct
mm_struct *mm)
struct aio_ring *ring;
spin_lock(&mm->ioctx_lock);
- table = rcu_dereference(mm->ioctx_table);
+ table = mm->ioctx_table;
while (1) {
if (table)
@@ -503,7 +503,7 @@ static int ioctx_add_table(struct kioctx *ctx, struct
mm_struct *mm)
table->nr = new_nr;
spin_lock(&mm->ioctx_lock);
- old = rcu_dereference(mm->ioctx_table);
+ old = mm->ioctx_table;
if (!old) {
rcu_assign_pointer(mm->ioctx_table, table);
@@ -579,10 +579,6 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
if (ctx->req_batch < 1)
ctx->req_batch = 1;
- err = ioctx_add_table(ctx, mm);
- if (err)
- goto out_cleanup_noerr;
-
/* limit the number of system wide aios */
spin_lock(&aio_nr_lock);
if (aio_nr + nr_events > (aio_max_nr * 2UL) ||
@@ -595,13 +591,18 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
percpu_ref_get(&ctx->users); /* io_setup() will drop this ref */
+ err = ioctx_add_table(ctx, mm);
+ if (err)
+ goto out_cleanup_put;
+
pr_debug("allocated ioctx %p[%ld]: mm=%p mask=0x%x\n",
ctx, ctx->user_id, mm, ctx->nr_events);
return ctx;
+out_cleanup_put:
+ percpu_ref_put(&ctx->users);
out_cleanup:
err = -EAGAIN;
-out_cleanup_noerr:
aio_free_ring(ctx);
out_freepcpu:
free_percpu(ctx->cpu);
@@ -626,7 +627,7 @@ static void kill_ioctx(struct mm_struct *mm, struct kioctx
*ctx)
struct kioctx_table *table;
spin_lock(&mm->ioctx_lock);
- table = rcu_dereference(mm->ioctx_table);
+ table = mm->ioctx_table;
WARN_ON(ctx != table->table[ctx->id]);
table->table[ctx->id] = NULL;
--
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