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Message-ID: <F792CF86EFE20D4AB8064279AFBA51C613E6B93B@HKNPRD3002MB017.064d.mgd.msft.net>
Date: Tue, 2 Dec 2014 05:33:25 +0000
From: Dexuan Cui <decui@...rosoft.com>
To: KY Srinivasan <kys@...rosoft.com>, Jason Wang <jasowang@...hat.com>
CC: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"driverdev-devel@...uxdriverproject.org"
<driverdev-devel@...uxdriverproject.org>,
"olaf@...fle.de" <olaf@...fle.de>,
"apw@...onical.com" <apw@...onical.com>,
"vkuznets@...hat.com" <vkuznets@...hat.com>,
Haiyang Zhang <haiyangz@...rosoft.com>
Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on transfer
failure
> -----Original Message-----
> From: KY Srinivasan
> Sent: Monday, December 1, 2014 23:55 PM
> To: Dexuan Cui; Jason Wang
> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; driverdev-
> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> vkuznets@...hat.com; Haiyang Zhang
> Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on transfer
> failure
>
>
>
> > -----Original Message-----
> > From: Dexuan Cui
> > Sent: Monday, December 1, 2014 3:01 AM
> > To: Jason Wang
> > Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; driverdev-
> > devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com; KY
> > Srinivasan; vkuznets@...hat.com; Haiyang Zhang
> > Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on transfer
> > failure
> >
> > > -----Original Message-----
> > > From: Jason Wang [mailto:jasowang@...hat.com]
> > > Sent: Monday, December 1, 2014 18:18 PM
> > > To: Dexuan Cui
> > > Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> > > driverdev- devel@...uxdriverproject.org; olaf@...fle.de;
> > > apw@...onical.com; KY Srinivasan; vkuznets@...hat.com; Haiyang
> Zhang
> > > Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on
> > > transfer failure
> > >
> > >
> > >
> > > On Mon, Dec 1, 2014 at 5:47 PM, Dexuan Cui <decui@...rosoft.com>
> > wrote:
> > > >> -----Original Message-----
> > > >> From: Jason Wang [mailto:jasowang@...hat.com]
> > > >> Sent: Monday, December 1, 2014 16:23 PM
> > > >> To: Dexuan Cui
> > > >> Cc: gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org;
> > > >> driverdev-
> > > >> devel@...uxdriverproject.org; olaf@...fle.de; apw@...onical.com;
> > > >> KY Srinivasan; vkuznets@...hat.com; Haiyang Zhang
> > > >> Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete message on
> > > >> transfer failure On Fri, Nov 28, 2014 at 7:54 PM, Dexuan Cui
> > > >> <decui@...rosoft.com>
> > > >> wrote:
> > > >> >> -----Original Message-----
> > > >> >> From: Jason Wang [mailto:jasowang@...hat.com] >> Sent:
> > > >> Friday, November 28, 2014 18:13 PM >> To: Dexuan Cui >> Cc:
> > > >> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; >>
> > > >> driverdev- >> devel@...uxdriverproject.org; olaf@...fle.de;
> > > >> apw@...onical.com; KY >> Srinivasan; vkuznets@...hat.com;
> Haiyang
> > > >> Zhang >> Subject: RE: [PATCH v3] hv: hv_fcopy: drop the obsolete
> > > >> message on >> transfer >> failure >> On Fri, Nov 28, 2014 at
> > > >> 4:36 PM, Dexuan Cui <decui@...rosoft.com> >> wrote:
> > > >> >> >> -----Original Message----- >> >> From: Jason Wang
> > > >> [mailto:jasowang@...hat.com] >> >> Sent: Friday, November 28,
> > > >> 2014 14:47 PM >> >> To: Dexuan Cui >> >> Cc:
> > > >> gregkh@...uxfoundation.org; linux-kernel@...r.kernel.org; >> >>
> > > >> driverdev- >> >> devel@...uxdriverproject.org; olaf@...fle.de;
> > > >> >> apw@...onical.com; KY >> >> Srinivasan; vkuznets@...hat.com;
> > > >> Haiyang Zhang >> >> Subject: Re: [PATCH v3] hv: hv_fcopy: drop
> > > >> the obsolete message >> on >> >> transfer >> >> failure >>
> > > >> >> On Thu, Nov 27, 2014 at 9:09 PM, Dexuan Cui >>
> > > >> <decui@...rosoft.com> >> >> wrote:
> > > >> >> >> > 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@...hat.com> >> >> > Cc:
> > > >> Vitaly Kuznetsov <vkuznets@...hat.com> >> >> > Cc: K. Y.
> > > >> Srinivasan <kys@...rosoft.com> >> >> > Signed-off-by: Dexuan Cui
> > > >> <decui@...rosoft.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.
> > > >> >> >> >
> > > >> >> >> > drivers/hv/hv_fcopy.c | 19 +++++++++++++++++++ >> >>
> > > >> > 1 file changed, 19 insertions(+) >> >> > >> >> > diff
> > > >> --git a/drivers/hv/hv_fcopy.c b/drivers/hv/hv_fcopy.c >> >> >
> > > >> index 23b2ce2..faa6ba6 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))
> > > >> >> >> > +;
> > > >> >> >>
> > > >> >> >> Sorry, I'm not quite understand how if () ; can help here.
> > > >> >> >>
> > > >> >> >> Btw, a question not relate to this patch.
> > > >> >> >>
> > > >> >> >> What happens if a daemon is resume from SIGSTOP and
> > > >> expires the >> >> check >> >> here?
> > > >> >> > Hi Jason,
> > > >> >> > My idea is: here we need down_trylock(), but in case we
> > > >> can't get >> the >> > semaphore, it's OK anyway:
> > > >> >> >
> > > >> >> > Scenario 1):
> > > >> >> > 1.1: when the daemon is blocked on the pread(), the daemon
> > > >> >> receives >> > SIGSTOP; >> > 1.2: the host user runs the
> > > >> PowerShell Copy-VMFile command; >> > 1.3.1: the driver reports
> > > >> the failure to the host user in 5s and >> > 1.3.2: the driver
> > > >> down()-es the semaphore; >> > 1.4: the daemon receives SIGCONT
> > > >> and it will be still blocked on >> the >> > pread().
> > > >> >> > Without the down_trylock(), in 1.4, the daemon can receive
> > > >> an >> > obsolete message.
> > > >> >> > NOTE: in this scenario, the daemon is not killed.
> > > >> >> >
> > > >> >> > Scenario 2):
> > > >> >> > In senario 1), if the daemon receives SIGCONT between 1.3.1
> > > >> and >> 1.3.2 >> > and >> > do down() in fcopy_read(), it will
> > > >> receive the message but:
> > > >> the
> > > >> >> > driver has
> > > >> >> > reported the failure to the host user and the driver's 1.3.2
> > > >> can't >> > get the >> > semaphore -- IMO this is acceptably OK,
> > > >> though in the VM, an >> > incomplete >> > file will be left
> > > >> there.
> > > >> >> > BTW, I think in the daemon's hv_start_fcopy() we should add
> > > >> a >> > close(target_fd) before open()-ing a new one.
> > > >> >>
> > > >> >> Right, but how about the case when resuming from SIGSTOP but
> > > >> no >> timeout?
> > > >> > Sorry, I don't understand this:
> > > >> > if no timeout, fcopy_read() will get the semaphore and
> > > >> fcopy_write()
> > > >> > will try to cancel fcopy_work.
> > > >>
> > > >> Yes.
> > > >> >
> > > >> >
> > > >> >> Looks like in this case userspace() may wait in
> > > >> down_interruptible()
> > > >> >> until timeout. We probably need something like this:
> > > >> >>
> > > >> >> if (down_interruptible(&fcopy_transaction.read_sema)) {
> > > >> >> up(&fcopy_transaction.read_sema);
> > > >> >> return -EINTR;
> > > >> >> }
> > > >> > until "timeout"?
> > > >> > if the daemon can't get the semaphore, it can only be wake by a
> > > >> > signal(the > daemon doesn't install handler, so by default most
> > > >> signals will kill > the daemon).
> > > >> > In case a signal waking up the daemon doesn't kill the daemon,
> > > >> why > should > we do up()?
> > > >>
> > > >> True, no need since we do down_trylock() in release().
> > > >>
> > > >> Btw, there's no EINTR handling in handling pread() return value,
> > > >> may add such one which should be useful for something like
> > > >> debugging.
> > > >>
> > > >> >
> > > >> >
> > > >> >>
> > > >> >> This should synchronize with the timeout work for sure.
> > > >> >> But how about only schedule it after this?
> > > >> >> It does not may sense to start the timer during interrupt >>
> > > >> since the file may not even opened and it may take time >> to
> > > >> handle signals?
> > > >> >>
> > > >> >> >
> > > >> >> >> >
> > > >> >> >> > +
> > > >> >> >> > }
> > > >> >> >> >
> > > >> >> >> > static int fcopy_handle_handshake(u32 version) >> >>
> > > >> > @@ -351,6 +363,13 @@ 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))
> > > >> >> >> > +;
> > > >> >> >>
> > > >> >> >> And this.
> > > >> >> >
> > > >> >> > Scenario 3):
> > > >> >> > When the daemon exits(e.g., SIGKILL received), if there is a
> > > >> >> > fcopy_work >> > pending (scheduled but not start to run
> > > >> yet), we should cancel the >> > work (as you suggested) and
> > > >> down() the semaphore, otherwise, the >> > obsolete message will
> > > >> be received by the next instance of the >> daemon.
> > > >> >>
> > > >> >> Yes
> > > >> >> >
> > > >> >> >
> > > >> >> > Scenario 4): in the driver's hv_fcopy_onchannelcallback():
> > > >> >> > schedule_delayed_work(&fcopy_work, 5*HZ);
> > > >> >> > ----> if fcopy_release() is running on another vcpu,
> > > >> just
> > > >> >> > before the next line?
> > > >> >> > fcopy_send_data();
> > > >> >> >
> > > >> >> > In this case, fcopy_release() can cancel fcopy_work, but >>
> > > >> > can't get the semaphore since it hasn't been up()-ed.
> > > >> >> > Hmm, in this case, fcopy_send_data() will do up() later,
> > > >> and
> > > >> >> we'll
> > > >> >> > buffer an obsolete message in the driver, and the message
> > > >> will be >> > fetched by the next instance of the daemon...
> > > >> >> >
> > > >> >> > Looks we need a spinlock here?
> > > >> >>
> > > >> >> Unless fcopy_release() can wait for all data for current
> > > >> transation >> to be received. Spinlock won't help.
> > > >> >>
> > > >> >> But an idea is let the daemon the handle such cases. E.g make
> > > >> sure >> the >> processing begins with START_COPY and end with
> > > >> COMPLETE/CANCEL_COPY.
> > > >> >> Drop all requests that does not start with START_COPY.
> > > >> >>
> > > >> >> Thought?
> > > >> > Good idea.
> > > >> > I also think we should reinforce the concept of state machine in
> > > >> the > daemon code.
> > > >>
> > > >> Yes, it needs.
> > > > I agree.
> > > > Obviously we can do something to make the daemon/driver work better
> > > > in the corner cases.
> > > >
> > > >> >
> > > >> > The daemon/driver communication has so many corner cases...
> > > >>
> > > >> Looks so, let's first address the issue mentioned in this patch.
> > > > OK.
> > > >
> > > >> I don't have any more comments other than changing
> > > >>
> > > >> if(down_trylock(&fcopy_transaction.read_sema))
> > > >> ;
> > > >>
> > > >> to
> > > >>
> > > >> down_trylock(&fcopy_transaction.read_sema);
> > > > Hi Jason,
> > > > This is to address Vitaly's comment in the bugzilla:
> > > > https://bugzilla.redhat.com/show_bug.cgi?id=1162100#c5
> > > >
> > > > down_trylock(&fcopy_transaction.read_sema) will
> > > >
> > > > "
> > > > produces the following compile warning:
> > > > drivers/hv/hv_fcopy.c: In function ‘fcopy_work_func’:
> > > > drivers/hv/hv_fcopy.c:95:2: warning: ignoring return value of
> > > > ‘down_trylock’, declared with attribute warn_unused_result
> > > > [-Wunused-result]
> > > > (void)down_trylock(&fcopy_transaction.read_sema);
> > > > "
> > > >
> > > > Actually I personally don't care about the warning, because we only
> > > > see it when we run some kind of code checker program. :-)
> > > >
> > > > I can change my v3 to the "normal" style you prefer, if there is no
> > > > strong objection from Vitaly?
> > >
> > > Ah, I see the point. Then no objection for this patch.
> > >
> > > Since Vitaly said he does not has objection.
> > >
> > > Acked-by: Jason Wang <jasowang@...hat.com>
> >
> > I realized non-trivial effort might be needed to better handle corner cases.
> > This is only the first step.
> >
> > E.g., I found a new corner case:
> > after we unload the hv_utils/fcopy driver, the fcopy daemon can exit and
> > fcopy_release() will be invoked -- at this time fcopy_release() has become
> > obsolete and invalid, and as a result, a kernel panic can happen: I did see
> the
> > panic once.
>
> You should not be able to unload the driver when there is still an open
> reference from the
> Daemon.
>
> K. Y
Hi KY, I'm able to reproduce the below issue every time:
(I ran the below in Ubuntu 14.10 but I think we're able to repro it in any distro):
1) start hv_fcopy_daemon and use ps to make sure it's running in the background;
2) kill -STOP `pidof hv_fcopy_daemon`, and use ps to make sure the daemon is in
the state of "Ts";
3) rmmod hv_utils # dexuan: this can runs fine.
4) kill -CONT `pidof hv_fcopy_daemon` and we see an oops at once:
[ 9699.421564] BUG: unable to handle kernel paging request at ffffffffc019c230
[ 9699.422701] IP: [<ffffffff811de294>] filp_close+0x24/0x70
[ 9699.423154] PGD 1c16067 PUD 1c18067 PMD 366d8067 PTE 0
[ 9699.423154] Oops: 0000 [#1] SMP
[ 9699.423154] Modules linked in: hv_utils rfcomm bnep bluetooth 6lowpan_iphc joydev hid_generic crct10dif_pclmul crc32_pclmul ghash_clmulni_intel aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd hid_hyperv serio_raw hid hyperv_keyboard hv_balloon mac_hid hyperv_fb i2c_piix4 parport_pc ppdev lp parport hv_storvsc psmouse floppy hv_vmbus tulip pata_acpi [last unloaded: hv_utils]
[ 9699.423154] CPU: 0 PID: 4659 Comm: hv_fcopy_daemon Not tainted 3.16.0-23-generic #31-Ubuntu
[ 9699.423154] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS 090006 05/23/2012
[ 9699.423154] task: ffff880019ce5bb0 ti: ffff8800c7be0000 task.ti: ffff8800c7be0000
[ 9699.423154] RIP: 0010:[<ffffffff811de294>] [<ffffffff811de294>] filp_close+0x24/0x70
[ 9699.423154] RSP: 0018:ffff8800c7be3e48 EFLAGS: 00010246
[ 9699.423154] RAX: ffffffffc019c1c0 RBX: ffff8800c7b9c200 RCX: ffff8800396548d8
[ 9699.423154] RDX: 0000000080000000 RSI: ffff880039654880 RDI: ffff8800c7b9c200
[ 9699.423154] RBP: ffff8800c7be3e60 R08: 0000000000000001 R09: 00000001802a0017
[ 9699.423154] R10: ffff88003de17640 R11: ffff880087963140 R12: 0000000000000000
[ 9699.423154] R13: ffff880039654880 R14: ffff880039654890 R15: 0000000000000004
[ 9699.423154] FS: 0000000000000000(0000) GS:ffff88003de00000(0000) knlGS:0000000000000000
[ 9699.423154] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 9699.423154] CR2: ffffffffc019c230 CR3: 0000000001c13000 CR4: 00000000001406f0
[ 9699.423154] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 9699.423154] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 9699.423154] Stack:
[ 9699.423154] 0000000000000001 0000000000000000 ffff880039654880 ffff8800c7be3ea0
[ 9699.423154] ffffffff811ff208 00000001034a4c80 ffff880019ce5bb0 ffff880039654880
[ 9699.423154] ffff880019ce6308 ffff8800126b8e00 ffff8800126b8e60 ffff8800c7be3ec8
[ 9699.423154] Call Trace:
[ 9699.423154] [<ffffffff811ff208>] put_files_struct+0x78/0xd0
[ 9699.423154] [<ffffffff811ff307>] exit_files+0x47/0x50
[ 9699.423154] [<ffffffff810725a7>] do_exit+0x357/0xab0
[ 9699.423154] [<ffffffff81072d83>] do_group_exit+0x43/0xc0
[ 9699.423154] [<ffffffff81072e14>] SyS_exit_group+0x14/0x20
[ 9699.423154] [<ffffffff81787ced>] system_call_fastpath+0x1a/0x1f
[ 9699.423154] Code: ff ff 0f 1f 44 00 00 0f 1f 44 00 00 55 48 89 e5 41 55 41 54 53 48 8b 47 38 48 89 fb 48 85 c0 74 46 48 8b 47 28 45 31 e4 49 89 f5 <48> 8b 40 70 48 85 c0 74 05 ff d0 41 89 c4 f6 43 45 40 75 16 4c
[ 9699.423154] RIP [<ffffffff811de294>] filp_close+0x24/0x70
[ 9699.423154] RSP <ffff8800c7be3e48>
[ 9699.423154] CR2: ffffffffc019c230
[ 9699.423154] ---[ end trace 0278723740833669 ]---
[ 9699.423154] Fixing recursive fault but reboot is needed!
I understand an administrator should not unload the driver before stopping the
daemon, but this could happen by accident.
-- Dexuan
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