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aio: add a iocb refcount

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This is needed to prevent races caused by the way the ->poll API works.
To avoid introducing overhead for other users of the iocbs we initialize
it to zero and only do refcount operations if it is non-zero in the
completion path.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: Avi Kivity <avi@scylladb.com>
This commit is contained in:
Christoph Hellwig 2018-07-24 11:36:37 +02:00
parent 7dda712818
commit 9018ccc453
1 changed files with 13 additions and 4 deletions
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17
fs/aio.c
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@ -18,6 +18,7 @@
#include <linux/export.h>
#include <linux/syscalls.h>
#include <linux/backing-dev.h>
#include <linux/refcount.h>
#include <linux/uio.h>
#include <linux/sched/signal.h>
@ -178,6 +179,7 @@ struct aio_kiocb {
struct list_head ki_list; /* the aio core uses this
* for cancellation */
refcount_t ki_refcnt;
/*
* If the aio_resfd field of the userspace iocb is not zero,
@ -1015,6 +1017,7 @@ static inline struct aio_kiocb *aio_get_req(struct kioctx *ctx)
percpu_ref_get(&ctx->reqs);
INIT_LIST_HEAD(&req->ki_list);
refcount_set(&req->ki_refcnt, 0);
req->ki_ctx = ctx;
return req;
out_put:
@ -1049,6 +1052,15 @@ out:
return ret;
}
static inline void iocb_put(struct aio_kiocb *iocb)
{
if (refcount_read(&iocb->ki_refcnt) == 0 ||
refcount_dec_and_test(&iocb->ki_refcnt)) {
percpu_ref_put(&iocb->ki_ctx->reqs);
kmem_cache_free(kiocb_cachep, iocb);
}
}
/* aio_complete
* Called when the io request on the given iocb is complete.
*/
@ -1118,8 +1130,6 @@ static void aio_complete(struct aio_kiocb *iocb, long res, long res2)
eventfd_ctx_put(iocb->ki_eventfd);
}
kmem_cache_free(kiocb_cachep, iocb);
/*
* We have to order our ring_info tail store above and test
* of the wait list below outside the wait lock. This is
@ -1130,8 +1140,7 @@ static void aio_complete(struct aio_kiocb *iocb, long res, long res2)
if (waitqueue_active(&ctx->wait))
wake_up(&ctx->wait);
percpu_ref_put(&ctx->reqs);
iocb_put(iocb);
}
/* aio_read_events_ring