[PATCH v4] aio: Don't inherit aio ring memory at fork

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

ChangeLog
	since V3
	  - remvoe BUG_ON
	  - change comment properly (thanks Jeff!)

	V1, V2: not posted

--------------------------------
Subject: [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.


Reviewed-by: 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
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 fs/aio.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

Index: b/fs/aio.c
===================================================================
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -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 +141,18 @@ static int aio_setup_ring(struct kioctx 
 		return -EAGAIN;
 	}
 
+	/*
+	 * The io_context is not inherited by the child after fork()
+	 * (see mm_init).  Therefore, it makes little sense for the
+	 * completion ring to be inherited.
+	 */
+	ret = sys_madvise(info->mmap_base, info->mmap_size, MADV_DONTFORK);
+	if (ret < 0) {
+		up_write(&ctx->mm->mmap_sem);
+		aio_free_ring(ctx);
+		return -EAGAIN;
+	}
+
 	dprintk("mmap address: 0x%08lx\n", info->mmap_base);
 	info->nr_pages = get_user_pages(current, ctx->mm,
 					info->mmap_base, nr_pages,