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Subject[RFC][PATCH v3 4/6] aio: Don't inherit aio ring memory at fork
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AIO folks, Am I missing anything?

===============
Subject: [RFC][PATCH] aio: Don't inherit aio ring memory at fork

Currently, mm_struct::ioctx_list member isn't copyed at fork. IOW aio context don't inherit at fork.
but only ring memory inherited. that's strange.

This patch mark DONTFORK to ring-memory too.
In addition, This patch has good side effect. it also fix "get_user_pages() vs fork" problem.

I think "man fork" also sould be changed. it only say

* The child does not inherit outstanding asynchronous I/O operations from
its parent (aio_read(3), aio_write(3)).

but aio_context_t (return value of io_setup(2)) also don't inherit in current implementaion.


Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Zach Brown <zach.brown@oracle.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-api@vger.kernel.org,
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
fs/aio.c | 8 ++++++++
1 file changed, 8 insertions(+)

Index: b/fs/aio.c
===================================================================
--- a/fs/aio.c 2009-04-12 23:33:59.000000000 +0900
+++ b/fs/aio.c 2009-04-13 02:56:05.000000000 +0900
@@ -106,6 +106,7 @@ static int aio_setup_ring(struct kioctx
unsigned nr_events = ctx->max_reqs;
unsigned long size;
int nr_pages;
+ int ret;

/* Compensate for the ring buffer's head/tail overlap entry */
nr_events += 2; /* 1 is required, 2 for good luck */
@@ -140,6 +141,13 @@ static int aio_setup_ring(struct kioctx
return -EAGAIN;
}

+ /*
+ * aio context doesn't inherit while fork. (see mm_init())
+ * Then, aio ring also mark DONTFORK.
+ */
+ ret = sys_madvise(info->mmap_base, info->mmap_size, MADV_DONTFORK);
+ BUG_ON(ret);
+
dprintk("mmap address: 0x%08lx\n", info->mmap_base);
info->nr_pages = get_user_pages(current, ctx->mm,
info->mmap_base, nr_pages,



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