[Drbd-dev] [PATCH] drbd: when change susp_uuid[NEW] to true, make sure susp_uuid[OLD] is false
Philipp Reisner
philipp.reisner at linbit.com
Fri Dec 8 09:17:50 CET 2023
Hello Zhengbing,
You are right! Thank you for being so persistent.
Do you want to send a patch formatted with git send-email that fixes
the condition as you suggested in your e-mail from Nov 27?
Otherwise, I will commit it in your name on Monday.
best regards,
Phil
On Thu, Dec 7, 2023 at 2:14 PM 黄正兵 <zhengbing.huang at easystack.cn> wrote:
>
>
> 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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