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author | Ciro Santilli <ciro.santilli@arm.com> | 2019-10-08 18:23:15 +0100 |
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committer | Ciro Santilli <ciro.santilli@arm.com> | 2019-10-24 12:59:42 +0000 |
commit | f60383d060ed82400526a47a1ba3182253e9f2f5 (patch) | |
tree | 041678967ea5eba59fc20b273ede9a479692c3e8 /src/base/SConscript | |
parent | 35b95c78ef45841af7a683a7582062384829ece9 (diff) | |
download | gem5-f60383d060ed82400526a47a1ba3182253e9f2f5.tar.xz |
cpu, sim-se: don't wake up threads that are awake in futex
FutexMap::wakeup is called when the futex(TGT_FUTEX_WAKE syscall is done.
FutexMap maintains a list of sleeping threads for each futex address
added on FutexMap::suspend, and entries are removed from the list
at FutexMap::wakeup.
The problem is that this system was not taking into account that threads
can be woken up by memory accesses to locked addresses via the path:
SimpleThread::activate
BaseSimpleCPU::wakeup
AbstractMemory::checkLockedAddrList
AbstractMemory::access
DRAMCtrl::recvAtomic
CoherentXBar::recvAtomicBackdoor
SimpleExecContext::writeMem
which happens on trivial pthread examples on ARM at least. The instruction
that locked memory in those test cases was LDAXR.
This could lead futex(TGT_FUTEX_WAKE to awake a thread that is already
awake but is first on the sleeping thread list, instead of a sleeping one,
which can lead all threads to incorrectly sleep and in turn to
"simulate() limit reached".
To implement this, ThreadContext::activate return now returns a boolean
that indicates if the state changed. suspend and halt are also modified
to also return a boolean in the same case for symmetry, although this is
not strictly necessary for the current patch.
Change-Id: Ia6b4d3e6148c64721d810b8f1fffaa208a394b06
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21606
Reviewed-by: Brandon Potter <Brandon.Potter@amd.com>
Maintainer: Brandon Potter <Brandon.Potter@amd.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Diffstat (limited to 'src/base/SConscript')
0 files changed, 0 insertions, 0 deletions