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hv: hv_fcopy: drop the obsolete message on transfer failure 

In the case the user-space daemon crashes, hangs or is killed, we
need to down the semaphore, otherwise, after the daemon starts next
time, the obsolete data in fcopy_transaction.message or
fcopy_transaction.fcopy_msg will be used immediately.

Cc: Jason Wang <jasowang@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Dexuan Cui 2015-01-14 01:55:10 -08:00 committed by Greg Kroah-Hartman
parent d61031ee8d
commit d9b1652947
1 changed files with 27 additions and 0 deletions
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27
drivers/hv/hv_fcopy.c
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@ -86,6 +86,18 @@ static void fcopy_work_func(struct work_struct *dummy)
* process the pending transaction.
*/
fcopy_respond_to_host(HV_E_FAIL);
/* In the case the user-space daemon crashes, hangs or is killed, we
* need to down the semaphore, otherwise, after the daemon starts next
* time, the obsolete data in fcopy_transaction.message or
* fcopy_transaction.fcopy_msg will be used immediately.
*
* NOTE: fcopy_read() happens to get the semaphore (very rare)? We're
* still OK, because we've reported the failure to the host.
*/
if (down_trylock(&fcopy_transaction.read_sema))
;
}
static int fcopy_handle_handshake(u32 version)
@ -344,6 +356,14 @@ static int fcopy_open(struct inode *inode, struct file *f)
return 0;
}
/* XXX: there are still some tricky corner cases, e.g.,
* 1) In a SMP guest, when fcopy_release() runs between
* schedule_delayed_work() and fcopy_send_data(), there is
* still a chance an obsolete message will be queued.
*
* 2) When the fcopy daemon is running, if we unload the driver,
* we'll notice a kernel oops when we kill the daemon later.
*/
static int fcopy_release(struct inode *inode, struct file *f)
{
/*
@ -351,6 +371,13 @@ static int fcopy_release(struct inode *inode, struct file *f)
*/
in_hand_shake = true;
opened = false;
if (cancel_delayed_work_sync(&fcopy_work)) {
/* We haven't up()-ed the semaphore(very rare)? */
if (down_trylock(&fcopy_transaction.read_sema))
;
fcopy_respond_to_host(HV_E_FAIL);
}
return 0;
}