From 178debe4350fefa38073cb43afe6282d9a513664 Mon Sep 17 00:00:00 2001 From: Martin Holst Swende Date: Tue, 2 Nov 2021 11:33:54 +0100 Subject: [PATCH] consensus/ethash: avoid runtime errors due to OOD on mmap writes (#23799) When we map a file for generating the DAG, we do a simple truncate to e.g. 1Gb. This is fine, even if we have nowhere near 1Gb disk available, as the actual file doesn't take up the full 1Gb, merely a few bytes. When we start generating into it, however, it eventually crashes with a unexpected fault address . This change fixes it (on linux systems) by using the Fallocate syscall, which preallocates suffcient space on disk to avoid that situation. Co-authored-by: Felix Lange --- consensus/ethash/ethash.go | 7 ++++-- consensus/ethash/mmap_help_linux.go | 35 ++++++++++++++++++++++++++++ consensus/ethash/mmap_help_other.go | 36 +++++++++++++++++++++++++++++ 3 files changed, 76 insertions(+), 2 deletions(-) create mode 100644 consensus/ethash/mmap_help_linux.go create mode 100644 consensus/ethash/mmap_help_other.go diff --git a/consensus/ethash/ethash.go b/consensus/ethash/ethash.go index ec06d02a54..4e33d99c8d 100644 --- a/consensus/ethash/ethash.go +++ b/consensus/ethash/ethash.go @@ -136,13 +136,16 @@ func memoryMapAndGenerate(path string, size uint64, lock bool, generator func(bu if err != nil { return nil, nil, nil, err } - if err = dump.Truncate(int64(len(dumpMagic))*4 + int64(size)); err != nil { + if err = ensureSize(dump, int64(len(dumpMagic))*4+int64(size)); err != nil { + dump.Close() + os.Remove(temp) return nil, nil, nil, err } // Memory map the file for writing and fill it with the generator mem, buffer, err := memoryMapFile(dump, true) if err != nil { dump.Close() + os.Remove(temp) return nil, nil, nil, err } copy(buffer, dumpMagic) @@ -358,7 +361,7 @@ func (d *dataset) generate(dir string, limit int, lock bool, test bool) { if err != nil { logger.Error("Failed to generate mapped ethash dataset", "err", err) - d.dataset = make([]uint32, dsize/2) + d.dataset = make([]uint32, dsize/4) generateDataset(d.dataset, d.epoch, cache) } // Iterate over all previous instances and delete old ones diff --git a/consensus/ethash/mmap_help_linux.go b/consensus/ethash/mmap_help_linux.go new file mode 100644 index 0000000000..b40a1dd25c --- /dev/null +++ b/consensus/ethash/mmap_help_linux.go @@ -0,0 +1,35 @@ +// Copyright 2021 The go-ethereum Authors +// This file is part of the go-ethereum library. +// +// The go-ethereum library is free software: you can redistribute it and/or modify +// it under the terms of the GNU Lesser General Public License as published by +// the Free Software Foundation, either version 3 of the License, or +// (at your option) any later version. +// +// The go-ethereum library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU Lesser General Public License for more details. +// +// You should have received a copy of the GNU Lesser General Public License +// along with the go-ethereum library. If not, see . + +//go:build linux +// +build linux + +package ethash + +import ( + "os" + + "golang.org/x/sys/unix" +) + +// ensureSize expands the file to the given size. This is to prevent runtime +// errors later on, if the underlying file expands beyond the disk capacity, +// even though it ostensibly is already expanded, but due to being sparse +// does not actually occupy the full declared size on disk. +func ensureSize(f *os.File, size int64) error { + // Docs: https://www.man7.org/linux/man-pages/man2/fallocate.2.html + return unix.Fallocate(int(f.Fd()), 0, 0, size) +} diff --git a/consensus/ethash/mmap_help_other.go b/consensus/ethash/mmap_help_other.go new file mode 100644 index 0000000000..8ad514ce42 --- /dev/null +++ b/consensus/ethash/mmap_help_other.go @@ -0,0 +1,36 @@ +// Copyright 2021 The go-ethereum Authors +// This file is part of the go-ethereum library. +// +// The go-ethereum library is free software: you can redistribute it and/or modify +// it under the terms of the GNU Lesser General Public License as published by +// the Free Software Foundation, either version 3 of the License, or +// (at your option) any later version. +// +// The go-ethereum library is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU Lesser General Public License for more details. +// +// You should have received a copy of the GNU Lesser General Public License +// along with the go-ethereum library. If not, see . + +//go:build !linux +// +build !linux + +package ethash + +import ( + "os" +) + +// ensureSize expands the file to the given size. This is to prevent runtime +// errors later on, if the underlying file expands beyond the disk capacity, +// even though it ostensibly is already expanded, but due to being sparse +// does not actually occupy the full declared size on disk. +func ensureSize(f *os.File, size int64) error { + // On systems which do not support fallocate, we merely truncate it. + // More robust alternatives would be to + // - Use posix_fallocate, or + // - explicitly fill the file with zeroes. + return f.Truncate(size) +}