On 12/22/2015 4:06 AM, Sebastian Andrzej Siewior wrote:
* Yang Shi | 2015-12-14 15:06:44 [-0800]:
Mainline kernel commit 959274753857efe9c5f1ba35fe727f51e9aa128d
("x86, traps: Track entry into and exit from IST context"), introduced
ist_enter which disables preemption uncondiontionally for both x86-64 and
x86-32. However, x86-32 does not have an IST and the stack still belongs to
the current task and there is no problem in scheduling out the task.
no no. So from a quick look I *assumed* you merged your v1 and revert of the
Steven's patch into one piece. But now I see that you don't disable preemption
64bit which means you revert upstream change.
No, I neither merged my v1 patch nor reverted Steven's patch.
Directed by Thomas's suggestion in v1 patch review, I looked into the
code further.
Currently, the code does:
ist_enter disables preemption unconditionally for both x86-64 and x86-32
(by mainline commit). So, for the x86-64 part, it is fine since the
preemption should be disabled because ist exception will use per CPU
stack and signal delay send is necessary.
But, disabling preemption on x86-32 is unnecessary since it doesn't have
ist stacks, so the v2 patch re-enables preemption for x86-32.
upstream commit 959274753857efe9c5f1ba35fe727f51e9aa128d ("x86, traps:
Track entry into and exit from IST context") commit log has more details
for the ist stacks.
So, #1) v1 patch is not needed anymore since x86-32 still doesn't need
signal delay send in v2, #2) don't need revert Steven's patch, the logic
is just changed slightly (#ifdef CONFIG_X86_64 --> #if
!defined(CONFIG_X86_64)) and adopted the mainline APIs.
So, this is definitely a new approach for fixing the same problem and
*not* an incremental patch.
Here is what happens:
- I drop your v2
- I merge your v1 with updated patch description
- I revert "x86: Do not disable preemption in int3 on 32bit". If someone
wants to skip the delayed signal on 32bit please address this upstream
first (that is skip the preempt_disable() on 32bit if it is not
required there).
- Yang Shi, please send a changelong if you send incremental patches.
Sorry for any inconvenience. I should made the comment clearer at the
first place even though it is not an incremental patch.
Thanks,
Yang
Sebastian
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