87f97c73d3
The following sequence of events can lead to the runtime attempting an out-of-bounds access on a stack barrier slice: 1. A SIGPROF comes in on a thread while the G on that thread is in _Gsyscall. The sigprof handler calls gentraceback, which saves a local copy of the G's stkbar slice. Currently the G has no stack barriers, so this slice is empty. 2. On another thread, the GC concurrently scans the stack of the goroutine being profiled (it considers it stopped because it's in _Gsyscall) and installs stack barriers. 3. Back on the sigprof thread, gentraceback comes across a stack barrier in the stack and attempts to look it up in its (zero length) copy of G's old stkbar slice, which causes an out-of-bounds access. This commit fixes this by adding a simple cas spin to synchronize the SIGPROF handler with stack barrier insertion. In general I would prefer that this synchronization be done through the G status, since that's how stack scans are otherwise synchronized, but adding a new lock is a much smaller change and G statuses are full of subtlety. Fixes #11863. Change-Id: Ie89614a6238bb9c6a5b1190499b0b48ec759eaf7 Reviewed-on: https://go-review.googlesource.com/12748 Reviewed-by: Russ Cox <rsc@golang.org> |
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