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aio: make aio_put_req() lockless 

Freeing a kiocb needed to touch the kioctx for three things:

 * Pull it off the reqs_active list
 * Decrementing reqs_active
 * Issuing a wakeup, if the kioctx was in the process of being freed.

This patch moves these to aio_complete(), for a couple reasons:

 * aio_complete() already has to issue the wakeup, so if we drop the
   kioctx refcount before aio_complete does its wakeup we don't have to
   do it twice.
 * aio_complete currently has to take the kioctx lock, so it makes sense
   for it to pull the kiocb off the reqs_active list too.
 * A later patch is going to change reqs_active to include unreaped
   completions - this will mean allocating a kiocb doesn't have to look
   at the ringbuffer. So taking the decrement of reqs_active out of
   kiocb_free() is useful prep work for that patch.

This doesn't really affect cancellation, since existing (usb) code that
implements a cancel function still calls aio_complete() - we just have
to make sure that aio_complete does the necessary teardown for cancelled
kiocbs.

It does affect code paths where we free kiocbs that were never
submitted; they need to decrement reqs_active and pull the kiocb off the
reqs_active list.  This occurs in two places: kiocb_batch_free(), which
is going away in a later patch, and the error path in io_submit_one.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Kent Overstreet <koverstreet@google.com>
Cc: Zach Brown <zab@redhat.com>
Cc: Felipe Balbi <balbi@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Asai Thambi S P <asamymuthupa@micron.com>
Cc: Selvan Mani <smani@micron.com>
Cc: Sam Bradshaw <sbradshaw@micron.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Benjamin LaHaise <bcrl@kvack.org>
Reviewed-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kent Overstreet 2013-05-07 16:18:39 -07:00 committed by Linus Torvalds
parent 1d98ebfccc
commit 11599ebac4
2 changed files with 36 additions and 54 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

86
fs/aio.c
View File

@ -89,7 +89,7 @@ struct kioctx {
spinlock_t ctx_lock;
int reqs_active;
atomic_t reqs_active;
struct list_head active_reqs; /* used for cancellation */
/* sys_io_setup currently limits this to an unsigned int */
@ -250,7 +250,7 @@ static void ctx_rcu_free(struct rcu_head *head)
static void __put_ioctx(struct kioctx *ctx)
{
unsigned nr_events = ctx->max_reqs;
BUG_ON(ctx->reqs_active);
BUG_ON(atomic_read(&ctx->reqs_active));
aio_free_ring(ctx);
if (nr_events) {
@ -284,7 +284,7 @@ static int kiocb_cancel(struct kioctx *ctx, struct kiocb *kiocb,
cancel = kiocb->ki_cancel;
kiocbSetCancelled(kiocb);
if (cancel) {
kiocb->ki_users++;
atomic_inc(&kiocb->ki_users);
spin_unlock_irq(&ctx->ctx_lock);
memset(res, 0, sizeof(*res));
@ -383,12 +383,12 @@ static void kill_ctx(struct kioctx *ctx)
kiocb_cancel(ctx, req, &res);
}
if (!ctx->reqs_active)
if (!atomic_read(&ctx->reqs_active))
goto out;
add_wait_queue(&ctx->wait, &wait);
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
while (ctx->reqs_active) {
while (atomic_read(&ctx->reqs_active)) {
spin_unlock_irq(&ctx->ctx_lock);
io_schedule();
set_task_state(tsk, TASK_UNINTERRUPTIBLE);
@ -406,9 +406,9 @@ out:
*/
ssize_t wait_on_sync_kiocb(struct kiocb *iocb)
{
while (iocb->ki_users) {
while (atomic_read(&iocb->ki_users)) {
set_current_state(TASK_UNINTERRUPTIBLE);
if (!iocb->ki_users)
if (!atomic_read(&iocb->ki_users))
break;
io_schedule();
}
@ -438,7 +438,7 @@ void exit_aio(struct mm_struct *mm)
printk(KERN_DEBUG
"exit_aio:ioctx still alive: %d %d %d\n",
atomic_read(&ctx->users), ctx->dead,
ctx->reqs_active);
atomic_read(&ctx->reqs_active));
/*
* We don't need to bother with munmap() here -
* exit_mmap(mm) is coming and it'll unmap everything.
@ -453,11 +453,11 @@ void exit_aio(struct mm_struct *mm)
}
/* aio_get_req
* Allocate a slot for an aio request. Increments the users count
* Allocate a slot for an aio request. Increments the ki_users count
* of the kioctx so that the kioctx stays around until all requests are
* complete. Returns NULL if no requests are free.
*
* Returns with kiocb->users set to 2. The io submit code path holds
* Returns with kiocb->ki_users set to 2. The io submit code path holds
* an extra reference while submitting the i/o.
* This prevents races between the aio code path referencing the
* req (after submitting it) and aio_complete() freeing the req.
@ -471,7 +471,7 @@ static struct kiocb *__aio_get_req(struct kioctx *ctx)
return NULL;
req->ki_flags = 0;
req->ki_users = 2;
atomic_set(&req->ki_users, 2);
req->ki_key = 0;
req->ki_ctx = ctx;
req->ki_cancel = NULL;
@ -512,9 +512,9 @@ static void kiocb_batch_free(struct kioctx *ctx, struct kiocb_batch *batch)
list_del(&req->ki_batch);
list_del(&req->ki_list);
kmem_cache_free(kiocb_cachep, req);
ctx->reqs_active--;
atomic_dec(&ctx->reqs_active);
}
if (unlikely(!ctx->reqs_active && ctx->dead))
if (unlikely(!atomic_read(&ctx->reqs_active) && ctx->dead))
wake_up_all(&ctx->wait);
spin_unlock_irq(&ctx->ctx_lock);
}
@ -545,7 +545,8 @@ static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
spin_lock_irq(&ctx->ctx_lock);
ring = kmap_atomic(ctx->ring_info.ring_pages[0]);
avail = aio_ring_avail(&ctx->ring_info, ring) - ctx->reqs_active;
avail = aio_ring_avail(&ctx->ring_info, ring) -
atomic_read(&ctx->reqs_active);
BUG_ON(avail < 0);
if (avail < allocated) {
/* Trim back the number of requests. */
@ -560,7 +561,7 @@ static int kiocb_batch_refill(struct kioctx *ctx, struct kiocb_batch *batch)
batch->count -= allocated;
list_for_each_entry(req, &batch->head, ki_batch) {
list_add(&req->ki_list, &ctx->active_reqs);
ctx->reqs_active++;
atomic_inc(&ctx->reqs_active);
}
kunmap_atomic(ring);
@ -583,10 +584,8 @@ static inline struct kiocb *aio_get_req(struct kioctx *ctx,
return req;
}
static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
static void kiocb_free(struct kiocb *req)
{
assert_spin_locked(&ctx->ctx_lock);
if (req->ki_filp)
fput(req->ki_filp);
if (req->ki_eventfd != NULL)
@ -596,40 +595,12 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
if (req->ki_iovec != &req->ki_inline_vec)
kfree(req->ki_iovec);
kmem_cache_free(kiocb_cachep, req);
ctx->reqs_active--;
if (unlikely(!ctx->reqs_active && ctx->dead))
wake_up_all(&ctx->wait);
}
/* __aio_put_req
* Returns true if this put was the last user of the request.
*/
static void __aio_put_req(struct kioctx *ctx, struct kiocb *req)
{
assert_spin_locked(&ctx->ctx_lock);
req->ki_users--;
BUG_ON(req->ki_users < 0);
if (likely(req->ki_users))
return;
list_del(&req->ki_list); /* remove from active_reqs */
req->ki_cancel = NULL;
req->ki_retry = NULL;
really_put_req(ctx, req);
}
/* aio_put_req
* Returns true if this put was the last user of the kiocb,
* false if the request is still in use.
*/
void aio_put_req(struct kiocb *req)
{
struct kioctx *ctx = req->ki_ctx;
spin_lock_irq(&ctx->ctx_lock);
__aio_put_req(ctx, req);
spin_unlock_irq(&ctx->ctx_lock);
if (atomic_dec_and_test(&req->ki_users))
kiocb_free(req);
}
EXPORT_SYMBOL(aio_put_req);
@ -677,9 +648,9 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
* - the sync task helpfully left a reference to itself in the iocb
*/
if (is_sync_kiocb(iocb)) {
BUG_ON(iocb->ki_users != 1);
BUG_ON(atomic_read(&iocb->ki_users) != 1);
iocb->ki_user_data = res;
iocb->ki_users = 0;
atomic_set(&iocb->ki_users, 0);
wake_up_process(iocb->ki_obj.tsk);
return;
}
@ -694,6 +665,8 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
*/
spin_lock_irqsave(&ctx->ctx_lock, flags);
list_del(&iocb->ki_list); /* remove from active_reqs */
/*
* cancelled requests don't get events, userland was given one
* when the event got cancelled.
@ -740,7 +713,8 @@ void aio_complete(struct kiocb *iocb, long res, long res2)
put_rq:
/* everything turned out well, dispose of the aiocb. */
__aio_put_req(ctx, iocb);
aio_put_req(iocb);
atomic_dec(&ctx->reqs_active);
/*
* We have to order our ring_info tail store above and test
@ -905,7 +879,7 @@ static int read_events(struct kioctx *ctx,
break;
/* Try to only show up in io wait if there are ops
* in flight */
if (ctx->reqs_active)
if (atomic_read(&ctx->reqs_active))
io_schedule();
else
schedule();
@ -1369,6 +1343,14 @@ static int io_submit_one(struct kioctx *ctx, struct iocb __user *user_iocb,
return 0;
out_put_req:
spin_lock_irq(&ctx->ctx_lock);
list_del(&req->ki_list);
spin_unlock_irq(&ctx->ctx_lock);
atomic_dec(&ctx->reqs_active);
if (unlikely(!atomic_read(&ctx->reqs_active) && ctx->dead))
wake_up_all(&ctx->wait);
aio_put_req(req); /* drop extra ref to req */
aio_put_req(req); /* drop i/o ref to req */
return ret;

4
include/linux/aio.h
View File

@ -49,7 +49,7 @@ struct kioctx;
*/
struct kiocb {
unsigned long ki_flags;
int ki_users;
atomic_t ki_users;
unsigned ki_key; /* id of this request */
struct file *ki_filp;
@ -96,7 +96,7 @@ static inline bool is_sync_kiocb(struct kiocb *kiocb)
static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
{
*kiocb = (struct kiocb) {
.ki_users = 1,
.ki_users = ATOMIC_INIT(1),
.ki_key = KIOCB_SYNC_KEY,
.ki_filp = filp,
.ki_obj.tsk = current,