| commit | b2482e481722357c6daa98ef074d8eaf8ac4baf3 | [log] [tgz] |
|---|---|---|
| author | Cherry Zhang <cherryyz@google.com> | Thu Nov 14 20:23:17 2019 -0500 |
| committer | Cherry Zhang <cherryyz@google.com> | Wed Nov 27 01:30:19 2019 +0000 |
| tree | 32ce92d105f52c29f4ff65c90ac3576bc85e831e | |
| parent | c3f149250e036f6bf77e7c9512dd3d57e1c78452 [diff] |
cmd/internal/obj: mark split-stack prologue nonpreemptible When there are both a synchronous preemption request (by clobbering the stack guard) and an asynchronous one (by signal), the running goroutine may observe the synchronous request first in stack bounds check, and go to the path of calling morestack. If the preemption signal arrives at this point before the call to morestack, the goroutine will be asynchronously preempted, entering the scheduler. When it is resumed, the scheduler clears the preemption request, unclobbers the stack guard. But the resumed goroutine will still call morestack, as it is already on its way. morestack will, as there is no preemption request, double the stack unnecessarily. If this happens multiple times, the stack may grow too big, although only a small amount is actually used. To fix this, we mark the stack bounds check and the call to morestack async-nonpreemptible, starting after the memory instruction (mostly a load, on x86 CMP with memory). Not done for Wasm as it does not support async preemption. Fixes #35470. Change-Id: Ibd7f3d935a3649b80f47539116ec9b9556680cf2 Reviewed-on: https://go-review.googlesource.com/c/go/+/207350 Reviewed-by: David Chase <drchase@google.com>
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