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Subject[PATCH 09/32] aio: add delayed cancel support
Date
The upcoming aio poll support would like to be able to complete the iocb
inline from the cancellation context, but that would cause a double lock
of ctx_lock as-is. Add a new delayed_cancel_reqs list of iocbs that
should be cancelled from outside the ctx_lock by calling the (re-)added
ki_cancel callback.

To make this safe aio_complete needs to check if this call should complete
the iocb, and to make that safe without much reordering a struct file
argument to put is padded to aio_complete.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/aio.c | 80 ++++++++++++++++++++++++++++++++++++--------------------
1 file changed, 51 insertions(+), 29 deletions(-)

diff --git a/fs/aio.c b/fs/aio.c
index be10dde20c8e..3afca506c7f0 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -138,7 +138,8 @@ struct kioctx {

struct {
spinlock_t ctx_lock;
- struct list_head active_reqs; /* used for cancellation */
+ struct list_head cancel_reqs;
+ struct list_head delayed_cancel_reqs;
} ____cacheline_aligned_in_smp;

struct {
@@ -171,6 +172,7 @@ struct aio_kiocb {
};

struct kioctx *ki_ctx;
+ int (*ki_cancel)(struct aio_kiocb *iocb);

struct iocb __user *ki_user_iocb; /* user's aiocb */
__u64 ki_user_data; /* user's data for completion */
@@ -178,6 +180,9 @@ struct aio_kiocb {
struct list_head ki_list; /* the aio core uses this
* for cancellation */

+ unsigned int flags; /* protected by ctx->ctx_lock */
+#define AIO_IOCB_CANCELLED (1 << 1)
+
/*
* If the aio_resfd field of the userspace iocb is not zero,
* this is the underlying eventfd context to deliver events to.
@@ -584,18 +589,23 @@ static void free_ioctx_users(struct percpu_ref *ref)
{
struct kioctx *ctx = container_of(ref, struct kioctx, users);
struct aio_kiocb *req;
+ LIST_HEAD(list);

spin_lock_irq(&ctx->ctx_lock);
-
- while (!list_empty(&ctx->active_reqs)) {
- req = list_first_entry(&ctx->active_reqs,
+ while (!list_empty(&ctx->cancel_reqs)) {
+ req = list_first_entry(&ctx->cancel_reqs,
struct aio_kiocb, ki_list);
list_del_init(&req->ki_list);
req->rw.ki_filp->f_op->cancel_kiocb(&req->rw);
}
-
+ list_splice_init(&ctx->delayed_cancel_reqs, &list);
spin_unlock_irq(&ctx->ctx_lock);

+ while (!list_empty(&list)) {
+ req = list_first_entry(&list, struct aio_kiocb, ki_list);
+ req->ki_cancel(req);
+ }
+
percpu_ref_kill(&ctx->reqs);
percpu_ref_put(&ctx->reqs);
}
@@ -715,7 +725,8 @@ static struct kioctx *ioctx_alloc(unsigned nr_events)
mutex_lock(&ctx->ring_lock);
init_waitqueue_head(&ctx->wait);

- INIT_LIST_HEAD(&ctx->active_reqs);
+ INIT_LIST_HEAD(&ctx->cancel_reqs);
+ INIT_LIST_HEAD(&ctx->delayed_cancel_reqs);

if (percpu_ref_init(&ctx->users, free_ioctx_users, 0, GFP_KERNEL))
goto err;
@@ -1032,25 +1043,34 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
return ret;
}

+#define AIO_COMPLETE_CANCEL (1 << 0)
+
/* aio_complete
* Called when the io request on the given iocb is complete.
*/
-static void aio_complete(struct aio_kiocb *iocb, long res, long res2)
+static void aio_complete(struct aio_kiocb *iocb, struct file *file, long res,
+ long res2, unsigned complete_flags)
{
struct kioctx *ctx = iocb->ki_ctx;
struct aio_ring *ring;
struct io_event *ev_page, *event;
unsigned tail, pos, head;
- unsigned long flags;
+ unsigned long flags;

if (!list_empty_careful(&iocb->ki_list)) {
- unsigned long flags;
-
spin_lock_irqsave(&ctx->ctx_lock, flags);
+ if (!(complete_flags & AIO_COMPLETE_CANCEL) &&
+ (iocb->flags & AIO_IOCB_CANCELLED)) {
+ spin_unlock_irqrestore(&ctx->ctx_lock, flags);
+ return;
+ }
+
list_del(&iocb->ki_list);
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}

+ fput(file);
+
/*
* Add a completion event to the ring buffer. Must be done holding
* ctx->completion_lock to prevent other code from messing with the tail
@@ -1384,8 +1404,7 @@ static void aio_complete_rw(struct kiocb *kiocb, long res, long res2)
file_end_write(kiocb->ki_filp);
}

- fput(kiocb->ki_filp);
- aio_complete(iocb, res, res2);
+ aio_complete(iocb, kiocb->ki_filp, res, res2, 0);
}

static int aio_prep_rw(struct kiocb *req, struct iocb *iocb)
@@ -1437,7 +1456,7 @@ static inline ssize_t aio_rw_ret(struct kiocb *req, ssize_t ret)
unsigned long flags;

spin_lock_irqsave(&ctx->ctx_lock, flags);
- list_add_tail(&iocb->ki_list, &ctx->active_reqs);
+ list_add_tail(&iocb->ki_list, &ctx->cancel_reqs);
spin_unlock_irqrestore(&ctx->ctx_lock, flags);
}
return ret;
@@ -1539,11 +1558,10 @@ static ssize_t aio_write(struct kiocb *req, struct iocb *iocb, bool vectored,
static void aio_fsync_work(struct work_struct *work)
{
struct fsync_iocb *req = container_of(work, struct fsync_iocb, work);
- int ret;
+ struct aio_kiocb *iocb = container_of(req, struct aio_kiocb, fsync);
+ struct file *file = req->file;

- ret = vfs_fsync(req->file, req->datasync);
- fput(req->file);
- aio_complete(container_of(req, struct aio_kiocb, fsync), ret, 0);
+ aio_complete(iocb, file, vfs_fsync(file, req->datasync), 0, 0);
}

static int aio_fsync(struct fsync_iocb *req, struct iocb *iocb, bool datasync)
@@ -1768,18 +1786,12 @@ COMPAT_SYSCALL_DEFINE3(io_submit, compat_aio_context_t, ctx_id,
}
#endif

-/* lookup_kiocb
- * Finds a given iocb for cancellation.
- */
static struct aio_kiocb *
-lookup_kiocb(struct kioctx *ctx, struct iocb __user *iocb)
+lookup_kiocb(struct list_head *list, struct iocb __user *iocb)
{
struct aio_kiocb *kiocb;

- assert_spin_locked(&ctx->ctx_lock);
-
- /* TODO: use a hash or array, this sucks. */
- list_for_each_entry(kiocb, &ctx->active_reqs, ki_list) {
+ list_for_each_entry(kiocb, list, ki_list) {
if (kiocb->ki_user_iocb == iocb)
return kiocb;
}
@@ -1801,6 +1813,7 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
{
struct kioctx *ctx;
struct aio_kiocb *kiocb;
+ LIST_HEAD(dummy);
int ret = -EINVAL;
u32 key;

@@ -1814,12 +1827,21 @@ SYSCALL_DEFINE3(io_cancel, aio_context_t, ctx_id, struct iocb __user *, iocb,
return -EINVAL;

spin_lock_irq(&ctx->ctx_lock);
- kiocb = lookup_kiocb(ctx, iocb);
+ kiocb = lookup_kiocb(&ctx->delayed_cancel_reqs, iocb);
if (kiocb) {
- list_del_init(&kiocb->ki_list);
- ret = kiocb->rw.ki_filp->f_op->cancel_kiocb(&kiocb->rw);
+ kiocb->flags |= AIO_IOCB_CANCELLED;
+ list_move_tail(&kiocb->ki_list, &dummy);
+ spin_unlock_irq(&ctx->ctx_lock);
+
+ ret = kiocb->ki_cancel(kiocb);
+ } else {
+ kiocb = lookup_kiocb(&ctx->cancel_reqs, iocb);
+ if (kiocb) {
+ list_del_init(&kiocb->ki_list);
+ ret = kiocb->rw.ki_filp->f_op->cancel_kiocb(&kiocb->rw);
+ }
+ spin_unlock_irq(&ctx->ctx_lock);
}
- spin_unlock_irq(&ctx->ctx_lock);

if (!ret) {
/*
--
2.17.0
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