> -----Original Message----- > From: Dexuan Cui [mailto:de...@microsoft.com] > Sent: Wednesday, January 14, 2015 1:55 AM > To: gre...@linuxfoundation.org; linux-ker...@vger.kernel.org; driverdev- > de...@linuxdriverproject.org; o...@aepfle.de; a...@canonical.com; > jasow...@redhat.com; vkuzn...@redhat.com > Cc: KY Srinivasan > Subject: [PATCH v4] 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 <jasow...@redhat.com> > Cc: Vitaly Kuznetsov <vkuzn...@redhat.com> > Cc: K. Y. Srinivasan <k...@microsoft.com> > Signed-off-by: Dexuan Cui <de...@microsoft.com> Signed-off-by: K. Y. Srinivasan <k...@microsoft.com> > > --- > > v2: I removed the "FCP" prefix as Greg asked. > > I also updated the output message a little: > "FCP: failed to acquire the semaphore" --> > "can not acquire the semaphore: it is benign" > > v3: I added the code in fcopy_release() as Jason Wang suggested. > I removed the pr_debug (it isn't so meaningful)and added a comment > instead. > > v4: this is a resend of v3, plus adding a comment before > fcopy_release(). > --- > drivers/hv/hv_fcopy.c | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c index > 23b2ce2..cd453e4 100644 > --- a/drivers/hv/hv_fcopy.c > +++ b/drivers/hv/hv_fcopy.c > @@ -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; > } > > -- > 1.9.1
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