RFC 2: MT safe fiber context switch on ARM #15582
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ysbaddaden
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kind:bug
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It's actually a bit more subtle: we must check for |
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@ysbaddaden This needs a conflict resolution. |
We need a store-store barrier between pushing the registers to the current stack and setting the resumable flag of the current fiber, otherwise the CPU is allowed to reorder the instructions at runtime and to store the resumable flag before or while storing the registers. This can happen for example: thread 1: enqueues current fiber A therad 1: swapcontext -> store resumable thread 1: is preempted thread 2: steals fiber A thread 2: resumes fiber A thread 2: loads registers => reads garbage => segfaults thread 1: stores registers (too late)
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@straight-shoota Rebased to drop the extracted first commit merged with #15585. No more conflicts. |
ysbaddaden
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Mar 28, 2025
straight-shoota
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Mar 28, 2025
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The ARM32 equivalent of #15581.
As stated in a comment the chosen assembly is compatible with armv6, but might not work on older architectures and it doesn't take advantage of armv7 supporting the
dmb ishinstruction.We might want to consider to integrate #14524 (comment) into the compiler, so we could add flags based on features, for example
armv7when any feature matches/\+v7(ve|r|m|em|s|k|)/.Note: I also reduced the duplicated assembly. Let's use the flags to wrap the FPU instructions intead of duplicating the assembly 4 times.Extracted as #15585 but the commit is still in this branch because I need it.