[Drbd-dev] [PATCH] drbd: when change susp_uuid[NEW] to true, make sure susp_uuid[OLD] is false
黄正兵
zhengbing.huang at easystack.cn
Thu Dec 7 14:14:37 CET 2023
Hi Philipp,Under the new condition, if the value of susp_uuid is {true, true}, the condition returns true.- if (create_new_uuid)
+ /* When susp_uuid goes from true to false, we just created a new
+ * current-uuid, it is pointless to do this one more time
+ */
+ if (create_new_uuid && !(susp_uuid[OLD] && !susp_uuid[NEW]))
set_bit(__NEW_CUR_UUID, &device->flags);if create_new_uuid is true, and susp_uuid is {true, true}, the condition is satisfied.
__NEW_CUR_UUID will be set.
best regards,
Zhengbing
From: Philipp Reisner <philipp.reisner at linbit.com>
Date: 2023-12-07 13:35:28
To: "黄正兵" <zhengbing.huang at easystack.cn>
Cc: dongsheng.yang at easystack.cn,drbd-dev at lists.linbit.com,Lars Ellenberg <lars.ellenberg at linbit.com>
Subject: Re: Re: Re: [PATCH] drbd: when change susp_uuid[NEW] to true, make sure susp_uuid[OLD] is false>Hello Zhengbing,
>
>no, I disagree. The code is good as it is since commit e31d63966fac73fc000b.
>
>Here is my explanation:
>
>IO is frozen because the resource lost quorum. The user changes the config
>and reduces the quorum setting to 1.
>
>The regular sequence is:
>
>1. in sanitize_state()
> susp_uuid = { false, true }
> DRBD keeps the resource suspended longer.
>
>2. in finish_state_change()
> it sets __NEW_CUR_UUIC and that moves to NEW_CUR_UUID later.
>
> in w_after_state_change()
>3a when susp_uuid goes from false -> true then drbd_uuid_new_current()
>3b Trigger another state change that sets susp_uuuid[NEW] back to false.
>
>1. sanitize_sate() susp_uuid = { true, false }
>2. in finish_state_change() nothing relevant happens
>3a no positive edge on susp_uuid no NEW_CUR_UUID bit nothing happens
>3b susp_uuid[NEW] == false -> nothing happens
>
>
>Now let us assume between 3a and 3b, another CPU does an unrelated
>state change that usually triggers a new current uuid:
>
>CPU0:
>1. in sanitize_state()
> susp_uuid = { false, true }
> DRBD keeps the resource suspended longer.
>
>2. in finish_state_change()
> it sets __NEW_CUR_UUIC and that moves to NEW_CUR_UUID later.
>
> in w_after_state_change()
>3a when susp_uuid goes from false -> true
> drbd_uuid_new_current()
>
> CPU1:
> Here, another thread starts another unrelated state change
> that again wants to set NEW_CUR_UUID. But let us go into the details.
>
> 1. in sanitize_state() susp_uuid = { true, true }
> 2. in finish_state_chanage() it does _NOT_ set __NEW_CUR_UUID
> because the condition only allows it, when we have a
> positive edge on susp_uuid (= susp_uuid = { false, true })
> But this time, it is susp_uuid = { true, true }. No edge.
> so __NEW_CUR_UUID stays 0 -> NEW_CUR_UUID stays 0
> 3a nothing, since no NEW_CUR_UUID
> 3b creates a state change to set susp_uuid[NEW] to false
>
>CPU: continues with w_after_state()
>3b Trigger another state change that sets susp_uuuid[NEW] back to false.
> This is an "empty state change" as it is false and does nothing.
>
>
>I think you have a mistake in your reasoning at T3.
>
>best regards,
> Philipp
>
>On Mon, Nov 27, 2023 at 3:48 PM 黄正兵 <zhengbing.huang at easystack.cn> wrote:
>>
>> Hi Philipp,
>>
>>
>> The third point about modification is that it may not cover all scenarios.
>>
>> In w_after_state_change(), between generating the new current_uuid and
>> clearing the susp_uuid, it is possible that another thread set the __NEW_CUR_UUID flag.
>>
>> The problem scenario is as follows:
>>
>> T1:
>> begin_state_change()
>> end_state_change()
>> __end_state_change()
>> ___end_state_change()
>> # susp_uuid value is {True, True}
>> T2: w_after_state_change()
>> drbd_uuid_new_current()
>>
>> T3:
>> begin_state_change()
>> # set __NEW_CUR_UUID flag
>> end_state_change()
>>
>> begin_state_change()
>> # set susp_uuid[NEW] = False
>> end_state_change()
>>
>> In the end, the NEW_CUR_UUID flag bit is generated and not cleaned up.
>>
>> Therefore, the third point about modification can be change to this:
>>
>> diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
>> index e35150340..2101c0ebc 100644
>> --- a/drbd/drbd_state.c
>> +++ b/drbd/drbd_state.c
>> @@ -2553,6 +2553,7 @@ static bool should_try_become_up_to_date(struct drbd_device *device, enum drbd_d
>> static void finish_state_change(struct drbd_resource *resource, const char *tag)
>> {
>> enum drbd_role *role = resource->role;
>> + bool *susp_uuid = resource->susp_uuid;
>> struct drbd_device *device;
>> struct drbd_connection *connection;
>> bool starting_resync = false;
>> @@ -2828,7 +2829,7 @@ static void finish_state_change(struct drbd_resource *resource, const char *tag)
>> if (role[OLD] == R_SECONDARY && role[NEW] == R_PRIMARY)
>> create_new_uuid = true;
>>
>> - if (create_new_uuid)
>> + if (create_new_uuid && !susp_uuid[OLD])
>> set_bit(__NEW_CUR_UUID, &device->flags);
>>
>> if (disk_state[NEW] != D_NEGOTIATING && get_ldev_if_state(device, D_DETACHING)) {
>>
>> best regards,
>> Zhengbing
>>
>>
>>
>>
>>
>> From: Philipp Reisner <philipp.reisner at linbit.com>
>> Date: 2023-11-25 15:47:16
>> To: "黄正兵" <zhengbing.huang at easystack.cn>
>> Cc: dongsheng.yang at easystack.cn,drbd-dev at lists.linbit.com
>> Subject: Re: Re: [PATCH] drbd: when change susp_uuid[NEW] to true, make sure susp_uuid[OLD] is false>Hi Zhengbing,
>> >
>> >Lars and I came up with this:
>> >
>> >commit e31d63966fac73fc000b584ccb2580016eccda17
>> >Author: Philipp Reisner <philipp.reisner at linbit.com>
>> >Date: Thu Nov 23 06:31:28 2023 +0100
>> >
>> > drbd: fix susp_uuid clearing
>> >
>> > I introduced susp_uuid for keeping a resource longer suspended for
>> > writing a new current-uuid.
>> > But in the following scenario, it failed to clear the susp_uuid bit:
>> >
>> > 1. The network connection between a primary and secondary node
>> > fails. The primary has the setting quorum=2. IO freezes on the
>> > primary node.
>> >
>> > 2. The user changes the quorum setting from 2 to one. The primary
>> > node generates a new current-uuid and clears the susp_uuid bit in
>> > a second state change.
>> >
>> > 3. If, during the second state change, another condition for creating
>> > a new current UUID evaluates to true, the code fails to clear the
>> > suspen_uuid bit.
>> >
>> > Fixing this in three places:
>> > 1. in sanitize_state(): Only set susp_uuid[NEW] if susp_uuid[OLD]
>> > was not set. That avoids it happening a second time after
>> > one iteration.
>> >
>> > 2. in w_after_state_chage(): Always end the cycle by setting clearing
>> > susp_uuid[NEW] if it is set. (Independently of susp_uuid[OLD].
>> >
>> > 3. in finish_sate_change(): Do not set NEW_CUR_UUID again if we are
>> > in this operation.
>> >
>> > Strictly speaking, (2) is unnecessary after (1), but I also do it
>> > since it shortens the code. Also, (3) alone would fix the issue.
>> >
>> > Fixes: d47f7456ab ("drbd: create new UUID before resuming IO upon
>> > regaining quorum")
>> >
>> > Co-developed-by: zhengbing.huang <zhengbing.huang at easystack.cn>
>> > Co-developed-by: Lars Ellenberg <lars.ellenberg at linbit.com>
>> >
>> >diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
>> >index e35150340..b884bb622 100644
>> >--- a/drbd/drbd_state.c
>> >+++ b/drbd/drbd_state.c
>> >@@ -2353,7 +2353,8 @@ static void sanitize_state(struct drbd_resource *resource)
>> > resource->susp_quorum[NEW] =
>> > resource->res_opts.on_no_quorum == ONQ_SUSPEND_IO ?
>> >!resource_has_quorum : false;
>> >
>> >- if (resource_is_suspended(resource, OLD) &&
>> >!resource_is_suspended(resource, NEW)) {
>> >+ if (!resource->susp_uuid[OLD] &&
>> >+ resource_is_suspended(resource, OLD) &&
>> >!resource_is_suspended(resource, NEW)) {
>> > idr_for_each_entry(&resource->devices, device, vnr) {
>> > if (test_bit(NEW_CUR_UUID, &device->flags)) {
>> > resource->susp_uuid[NEW] = true;
>> >@@ -2553,6 +2554,7 @@ static bool should_try_become_up_to_date(struct
>> >drbd_device *device, enum drbd_d
>> >static void finish_state_change(struct drbd_resource *resource, const char *tag)
>> >{
>> > enum drbd_role *role = resource->role;
>> >+ bool *susp_uuid = resource->susp_uuid;
>> > struct drbd_device *device;
>> > struct drbd_connection *connection;
>> > bool starting_resync = false;
>> >@@ -2828,7 +2830,10 @@ static void finish_state_change(struct
>> >drbd_resource *resource, const char *tag)
>> > if (role[OLD] == R_SECONDARY && role[NEW] == R_PRIMARY)
>> > create_new_uuid = true;
>> >
>> >- if (create_new_uuid)
>> >+ /* When susp_uuid goes from true to false, we just created a new
>> >+ * current-uuid, it is pointless to do this one more time
>> >+ */
>> >+ if (create_new_uuid && !(susp_uuid[OLD] && !susp_uuid[NEW]))
>> > set_bit(__NEW_CUR_UUID, &device->flags);
>> >
>> > if (disk_state[NEW] != D_NEGOTIATING &&
>> >get_ldev_if_state(device, D_DETACHING)) {
>> >@@ -4189,7 +4194,7 @@ static int w_after_state_change(struct drbd_work
>> >*w, int unused)
>> > still_connected = true;
>> > }
>> >
>> >- if (!susp_uuid[OLD] && susp_uuid[NEW]) {
>> >+ if (susp_uuid[NEW]) {
>> > unsigned long irq_flags;
>> >
>> > begin_state_change(resource, &irq_flags, CS_VERBOSE);
>> >
>> >On Thu, Nov 23, 2023 at 9:48 AM 黄正兵 <zhengbing.huang at easystack.cn> wrote:
>> >>
>> >> Hi Philipp,
>> >>
>> >> Such modifications may cause new problems.
>> >>
>> >> If, during the second state change, the NEW_CUR_UUID flag was not cleared.
>> >> clears the susp_uuid bit in a thirdly state change.
>> >>
>> >> Eventually, it becomes an endless cycle.
>> >>
>> >> So, is it possible to add the following modifications：
>> >>
>> >> diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
>> >> index 2fbd0b1..6bd6431 100644
>> >> --- a/drbd/drbd_state.c
>> >> +++ b/drbd/drbd_state.c
>> >> @@ -3938,9 +3938,13 @@ static int w_after_state_change(struct drbd_work *w, int unused)
>> >> drbd_maybe_khelper(device, connection, "disconnected");
>> >> }
>> >>
>> >> - if (!susp_uuid[OLD] && susp_uuid[NEW] &&
>> >> - test_and_clear_bit(NEW_CUR_UUID, &device->flags))
>> >> - new_current_uuid = true;
>> >> + if (susp_uuid[NEW]) {
>> >> + if (susp_uuid[OLD])
>> >> + clear_bit(NEW_CUR_UUID, &device->flags);
>> >> + else if (test_and_clear_bit(NEW_CUR_UUID, &device->flags))) {
>> >> + new_curr_uuid = true;
>> >> + }
>> >> + }
>> >>
>> >> if (new_current_uuid)
>> >> drbd_uuid_new_current(device, false);
>> >>
>> >> best regards,
>> >> Zhengbing
>> >>
>> >>
>> >>
>> >>
>> >>
>> >> From: Philipp Reisner <philipp.reisner at linbit.com>
>> >> Date: 2023-11-23 14:06:30
>> >> To: "zhengbing.huang" <zhengbing.huang at easystack.cn>
>> >> Cc: drbd-dev at lists.linbit.com,joel.colledge at linbit.com
>> >> Subject: Re: [PATCH] drbd: when change susp_uuid[NEW] to true, make sure susp_uuid[OLD] is false>Hello Zhengbing,
>> >> >
>> >> >Thank you for pointing this out. I created a little bit different patch.
>> >> >First, the sanitize_state() function should clean up the new state,
>> >> >but I think it should never change the old state.
>> >> >It can not rewrite history.
>> >> >Second, we do not want to create two new current-uuids while I/O is frozen.
>> >> >
>> >> > drbd: fix susp_uuid clearing
>> >> >
>> >> > I introduced susp_uuid for keeping a resource longer suspended for
>> >> > writing a new current-uuid.
>> >> > But in the following scenario, it failed to clear the susp_uuid bit:
>> >> >
>> >> > 1. The network connection between a primary and secondary node
>> >> > fails. The primary has the setting quorum=2. IO freezes on the
>> >> > primary node.
>> >> >
>> >> > 2. The user changes the quorum setting from 2 to one. The primary
>> >> > node generates a new current-uuid and clears the susp_uuid bit in a
>> >> > second state change.
>> >> >
>> >> > 3. If, during the second state change, another condition for creating
>> >> > a new current UUID evaluates to true, the code fails to clear the
>> >> > suspen_uuid bit.
>> >> >
>> >> > The second attempt to create a new current-uuid gets ignored since it
>> >> > is pointless to create two current-uuids while I/O is frozen.
>> >> >
>> >> > Fixes: d47f7456ab ("drbd: create new UUID before resuming IO upon
>> >> > regaining quorum")
>> >> >
>> >> > Co-developed-by: zhengbing.huang <zhengbing.huang at easystack.cn>
>> >> >
>> >> >diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
>> >> >index e35150340..316d3fd39 100644
>> >> >--- a/drbd/drbd_state.c
>> >> >+++ b/drbd/drbd_state.c
>> >> >@@ -4189,7 +4189,7 @@ static int w_after_state_change(struct drbd_work
>> >> >*w, int unused)
>> >> > still_connected = true;
>> >> > }
>> >> >
>> >> >- if (!susp_uuid[OLD] && susp_uuid[NEW]) {
>> >> >+ if (susp_uuid[NEW]) {
>> >> > unsigned long irq_flags;
>> >> >
>> >> > begin_state_change(resource, &irq_flags, CS_VERBOSE);
>> >> >
>> >> >
>> >> >I give this to internal review for merging.
>> >> >
>> >> >best regards,
>> >> > Philipp
>> >> >
>> >> >
>> >> >On Wed, Nov 22, 2023 at 4:25 AM zhengbing.huang
>> >> ><zhengbing.huang at easystack.cn> wrote:
>> >> >>
>> >> >> The problem scenario is as follows:
>> >> >>
>> >> >> 1. drbd is built on two nodes, role is primary and secondary, quorum is 2.
>> >> >> then drbd's network fails. IO will be suspended.
>> >> >> 2. primary modify quorum to 1, during this state change,
>> >> >> drbd will set susp_uuid[NEW] to true and generate a new UUID.
>> >> >> 3. then in w_after_state_change, start the second state change,
>> >> >> set susp_uuid[NEW] to false. but during the second state change,
>> >> >> it's possible to find NEW_CUR_UUID flag was set by others.
>> >> >> then sanitize_state() will set susp_uuid[NEW] to true.
>> >> >>
>> >> >> Finally susp_uuid value is {true, true}, IO is frozen.
>> >> >> And there is no way to set susp_uuid to false after that.
>> >> >>
>> >> >> So, while susp_uuid[NEW] is set to true, we want susp_uuid[OLD] to be false.
>> >> >>
>> >> >> Fixes: d47f7456ab ("drbd: create new UUID before resuming IO upon regaining quorum")
>> >> >> Signed-off-by: zhengbing.huang <zhengbing.huang at easystack.cn>
>> >> >> ---
>> >> >> drbd/drbd_state.c | 1 +
>> >> >> 1 file changed, 1 insertion(+)
>> >> >>
>> >> >> diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
>> >> >> index e35150340..0dedd2dae 100644
>> >> >> --- a/drbd/drbd_state.c
>> >> >> +++ b/drbd/drbd_state.c
>> >> >> @@ -2356,6 +2356,7 @@ static void sanitize_state(struct drbd_resource *resource)
>> >> >> if (resource_is_suspended(resource, OLD) && !resource_is_suspended(resource, NEW)) {
>> >> >> idr_for_each_entry(&resource->devices, device, vnr) {
>> >> >> if (test_bit(NEW_CUR_UUID, &device->flags)) {
>> >> >> + resource->susp_uuid[OLD] = false;
>> >> >> resource->susp_uuid[NEW] = true;
>> >> >> break;
>> >> >> }
>> >> >> --
>> >> >> 2.17.1
>> >> >>
>> >>
>> >>
>>
>>
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