hv: hv_fcopy: drop the obsolete message on transfer failure

PATCH Superseded Dexuan Cui 2 participants 5 messages Nov 27, 2014 Hyper-V/Azure core and drivers

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Dexuan Cui

author maintainer

2014-11-27 06:22 UTC #0 lore raw

PATCH v2 1/1 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.

Reviewed-by Vitaly Kuznetsov <[email protected]>

Cc K. Y. Srinivasan <[email protected]>

Signed-off-by Dexuan Cui <[email protected]>

---

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"

 drivers/hv/hv_fcopy.c | 9 +++++++++
 1 file changed, 9 insertions(+)

drivers/hv/hv_fcopy.c +9 -0

index 23b2ce2..c518ad9 100644
@@ -86,6 +86,15 @@ 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.
+	 */
+	if (down_trylock(&fcopy_transaction.read_sema))
+		pr_debug("can not acquire the semaphore: it is benign\n");
+
 }
 
 static int fcopy_handle_handshake(u32 version)

Signature · 1 line

1.9.1

Jason Wang

2014-11-27 07:14 UTC #1 lore raw

----- Original Message -----

Quoted 24 lines

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.
Reviewed-by Vitaly Kuznetsov <[email protected]>
Cc K. Y. Srinivasan <[email protected]>
Signed-off-by Dexuan Cui <[email protected]>
---
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"
 drivers/hv/hv_fcopy.c | 9 +++++++++
 1 file changed, 9 insertions(+)
drivers/hv/hv_fcopy.c +0 -0
index 23b2ce2..c518ad9 100644

drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy) · line 94

Quoted 9 lines

drivers/hv/hv_fcopy.c +6 -0

@@ -86,6 +86,15 @@ 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.
+	 */

Looks still racy, what happens if the daemon start before down_trylock() but after fcopy_respont_to_host() here?

drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy) · line 96

Quoted 2 lines

drivers/hv/hv_fcopy.c +2 -0

+	if (down_trylock(&fcopy_transaction.read_sema))
+		pr_debug("can not acquire the semaphore: it is benign\n");

typo

Quoted 13 lines

drivers/hv/hv_fcopy.c +1 -1
+
 }
 
 static int fcopy_handle_handshake(u32 version)
--
1.9.1
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Dexuan Cui

author maintainer

2014-11-27 08:51 UTC #2 lore raw

Quoted 42 lines

-----Original Message-----
From: Jason Wang [mailto:[email protected]]
Sent: Thursday, November 27, 2014 15:15 PM
To: Dexuan Cui
Cc: [email protected]; [email protected]; driverdev- [email protected]; [email protected]; [email protected]; KY Srinivasan; [email protected]; Haiyang Zhang
Subject: Re: [PATCH v2] hv: hv_fcopy: drop the obsolete message on transfer failure
----- Original Message -----
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct
Quoted 24 lines
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.
Reviewed-by Vitaly Kuznetsov <[email protected]>
Cc K. Y. Srinivasan <[email protected]>
Signed-off-by Dexuan Cui <[email protected]>
---
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"
 drivers/hv/hv_fcopy.c | 9 +++++++++
 1 file changed, 9 insertions(+)
drivers/hv/hv_fcopy.c +0 -0
index 23b2ce2..c518ad9 100644
@@ -86,6 +86,15 @@ static void fcopy_work_func(struct work_struct
*dummy)
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy)
Quoted 6 lines
drivers/hv/hv_fcopy.c +3 -0
 	 * 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

Quoted 6 lines

drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy) · line 94
Quoted 3 lines
drivers/hv/hv_fcopy.c +3 -0
+	 * time, the obsolete data in fcopy_transaction.message or
+	 * fcopy_transaction.fcopy_msg will be used immediately.
+	 */
Looks still racy, what happens if the daemon start before down_trylock() but after fcopy_respont_to_host() here?

Jason,
Thanks for pointing this out!
IMO we can resolve this by adding down_trylock() in fcopy_release(). What's your opinion?

Quoted 7 lines

drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy) · line 96
Quoted 3 lines
drivers/hv/hv_fcopy.c +2 -0
+	if (down_trylock(&fcopy_transaction.read_sema))
+		pr_debug("can not acquire the semaphore: it is benign\n");
typo
Quoted 2 lines
drivers/hv/hv_fcopy.c +1 -0
+
 }

Sorry -- what typo do you mean?

Thanks,
-- Dexuan ��{.n�+��+%��ݶ��w��{.n�+��{��G��{ay�ʇڙ�,j��f��h��z_�(�階�ݢj"��m��G��?��&��~��iO��z��v�^�m��?�I�

Jason Wang

2014-11-27 09:01 UTC #3 lore raw

Quoted 51 lines · Dexuan Cui

Quoted 51 lines
-----Original Message-----
From: Jason Wang [mailto:[email protected]]
Sent: Thursday, November 27, 2014 15:15 PM
To: Dexuan Cui
Cc: [email protected]; [email protected];
driverdev-
[email protected]; [email protected]; [email protected]; KY Srinivasan; [email protected]; Haiyang Zhang
Subject: Re: [PATCH v2] hv: hv_fcopy: drop the obsolete message on
transfer
failure
----- Original Message -----
Quoted 2 lines
In the case the user-space daemon crashes, hangs or is killed, we need to down the semaphore, otherwise, after the daemon starts
next
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct
Quoted 22 lines
time, the obsolete data in fcopy_transaction.message or fcopy_transaction.fcopy_msg will be used immediately.
Reviewed-by Vitaly Kuznetsov <[email protected]>
Cc K. Y. Srinivasan <[email protected]>
Signed-off-by Dexuan Cui <[email protected]>
---
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"
 drivers/hv/hv_fcopy.c | 9 +++++++++
 1 file changed, 9 insertions(+)
drivers/hv/hv_fcopy.c +0 -0
index 23b2ce2..c518ad9 100644
@@ -86,6 +86,15 @@ static void fcopy_work_func(struct work_struct
*dummy)
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy)
Quoted 5 lines
drivers/hv/hv_fcopy.c +2 -0
 	 * process the pending transaction.
 	 */
 	fcopy_respond_to_host(HV_E_FAIL);
+
+	/* In the case the user-space daemon crashes, hangs or is 
killed, we
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct · line 91
Quoted 1 line
drivers/hv/hv_fcopy.c +1 -0
+	 * need to down the semaphore, otherwise, after the daemon 
starts
next
Quoted 3 lines
drivers/hv/hv_fcopy.c +3 -0
+	 * time, the obsolete data in fcopy_transaction.message or
+	 * fcopy_transaction.fcopy_msg will be used immediately.
+	 */

Quoted 7 lines

Quoted 3 lines
Looks still racy, what happens if the daemon start before
down_trylock()
but after fcopy_respont_to_host() here?
Jason,
Thanks for pointing this out!
IMO we can resolve this by adding down_trylock() in fcopy_release(). What's your opinion?

Looks better and need to cancel the timeout also here?

Quoted 10 lines

Quoted 9 lines
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy) · line 96
Quoted 5 lines
drivers/hv/hv_fcopy.c +2 -0
+	if (down_trylock(&fcopy_transaction.read_sema))
+		pr_debug("can not acquire the semaphore: it is benign\n");
typo
Quoted 2 lines
drivers/hv/hv_fcopy.c +1 -0
+
 }
Sorry -- what typo do you mean?

s/benign/begin/ ?

Quoted 4 lines

Thanks,
-- Dexuan �NrybXǧv^)޺{.n+{zXܨ}Ơz&j:+vzZ++zfh~izw?&)ߢf^jǫym@Aa0hi

Dexuan Cui

author maintainer

2014-11-27 11:44 UTC #4 lore raw

Quoted 64 lines

-----Original Message-----
From: Jason Wang [mailto:[email protected]]
Sent: Thursday, November 27, 2014 17:01 PM
To: Dexuan Cui
Cc: [email protected]; [email protected]; driverdev- [email protected]; [email protected]; [email protected]; KY Srinivasan; [email protected]; Haiyang Zhang
Subject: RE: [PATCH v2] hv: hv_fcopy: drop the obsolete message on transfer failure
Quoted 54 lines · Dexuan Cui
Quoted 54 lines
-----Original Message-----
From: Jason Wang [mailto:[email protected]]
Sent: Thursday, November 27, 2014 15:15 PM
To: Dexuan Cui
Cc: [email protected]; [email protected];
driverdev-
[email protected]; [email protected]; [email protected]; KY Srinivasan; [email protected]; Haiyang Zhang
Subject: Re: [PATCH v2] hv: hv_fcopy: drop the obsolete message on
transfer
failure
----- Original Message -----
Quoted 2 lines
In the case the user-space daemon crashes, hangs or is killed, we need to down the semaphore, otherwise, after the daemon starts
next
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct
Quoted 22 lines
time, the obsolete data in fcopy_transaction.message or fcopy_transaction.fcopy_msg will be used immediately.
Reviewed-by Vitaly Kuznetsov <[email protected]>
Cc K. Y. Srinivasan <[email protected]>
Signed-off-by Dexuan Cui <[email protected]>
---
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"
 drivers/hv/hv_fcopy.c | 9 +++++++++
 1 file changed, 9 insertions(+)
drivers/hv/hv_fcopy.c +0 -0
index 23b2ce2..c518ad9 100644
@@ -86,6 +86,15 @@ static void fcopy_work_func(struct work_struct
*dummy)
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy)
Quoted 5 lines
drivers/hv/hv_fcopy.c +2 -0
 	 * process the pending transaction.
 	 */
 	fcopy_respond_to_host(HV_E_FAIL);
+
+	/* In the case the user-space daemon crashes, hangs or is
killed, we
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct · line 91
Quoted 1 line
drivers/hv/hv_fcopy.c +1 -0
+	 * need to down the semaphore, otherwise, after the daemon
starts
next
drivers/hv/hv_fcopy.c static void fcopy_work_func(struct work_struct *dummy) · line 94
Quoted 3 lines
drivers/hv/hv_fcopy.c +3 -0
+	 * time, the obsolete data in fcopy_transaction.message or
+	 * fcopy_transaction.fcopy_msg will be used immediately.
+	 */
Looks still racy, what happens if the daemon start before
down_trylock()
but after fcopy_respont_to_host() here?

Quoted 7 lines

Quoted 4 lines
Jason,
Thanks for pointing this out!
IMO we can resolve this by adding down_trylock() in fcopy_release(). What's your opinion?
Looks better and need to cancel the timeout also here?

OK, let me post a v3.

Quoted 6 lines

Quoted 6 lines
Quoted 6 lines
Quoted 5 lines
drivers/hv/hv_fcopy.c +2 -0
+	if (down_trylock(&fcopy_transaction.read_sema))
+		pr_debug("can not acquire the semaphore: it is benign\n");

Quoted 6 lines

Quoted 4 lines
Quoted 3 lines
typo
Quoted 2 lines
drivers/hv/hv_fcopy.c +1 -0
+
 }
Sorry -- what typo do you mean?
s/benign/begin/ ?

I meant the issue(can't get the semaphore) is benign.

I think we can just remove the message, as KY suggested. Instead, I'll add a comment for it.

Thanks,
-- Dexuan

��{.n�+��+%��ݶ��w��{.n�+��{��G��{ay�ʇڙ�,j��f��h��z_�(�階�ݢj"��m��G��?��&��~��iO��z��v�^�m��?�I�