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seL4_TCB_SetSchedParams: inconsistency between API reference and implementation #1311

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alwin-joshy opened this issue Aug 22, 2024 · 1 comment · May be fixed by #1312
Open

seL4_TCB_SetSchedParams: inconsistency between API reference and implementation #1311

alwin-joshy opened this issue Aug 22, 2024 · 1 comment · May be fixed by #1312

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@alwin-joshy
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For the seL4_TCB_SetSchedParams (MCS) invocation, the API reference states the following about the sched_context parameter

If the scheduling context is already bound to a notification or TCB that is not this TCB this operation will fail. Similarly, if this TCB is already bound to a scheduling context that is not this scheduling context, this will also fail.

This does not correspond to the implementation, which adheres to the following:

If the scheduling context is already bound to a notification or TCB, this operation will fail. Similarly, if this TCB is already bound to a scheduling context, this will also fail.

In other words, the operation will fail if the scheduling context passed in is the one that is already bound to the TCB.
@Indanz
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Indanz commented Aug 22, 2024

Indeed it does. Practically that means that seL4_TCB_SetSchedParams can only be called once when creating the TCB for the first time and that it's useless to update parameters later on.

invokeTCB_ThreadControlSched does have a check sc != target->tcbSchedContext, so I think the fix is to add the same exception to decodeSetSchedParams and leave the the API reference as it is.

@alwin-joshy alwin-joshy linked a pull request Aug 23, 2024 that will close this issue
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TCB_SetSchedParams: Change to match API reference alwin-joshy/seL4
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@alwin-joshy @Indanz