From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 07E50C5DF81 for ; Wed, 19 Aug 2026 23:11:38 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 2714C6B00B9; Wed, 19 Aug 2026 19:11:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 248DA6B00BA; Wed, 19 Aug 2026 19:11:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 15EFD6B00BB; Wed, 19 Aug 2026 19:11:37 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id E3CBB6B00B9 for ; Wed, 19 Aug 2026 19:11:36 -0400 (EDT) Received: from smtpin11.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 75533C0678 for ; Wed, 19 Aug 2026 23:11:36 +0000 (UTC) X-FDA: 85119567792.11.747187D Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf13.hostedemail.com (Postfix) with ESMTP id B84B72000C for ; Wed, 19 Aug 2026 23:11:34 +0000 (UTC) Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="l/gkZ57m"; spf=pass (imf13.hostedemail.com: domain of brauner@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=brauner@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1787181094; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=72gFO+JEMFm/mE5KyMl3szngZahRJUcU2+ZTWkuKUzQ=; b=GedaPn+TmD0AugApaeu5vYWywfno2UVUcKgLmsxVixsLXwlWbnxtncIKBIYMcIMxDMi2fD RDla1/5s8DbR1c7MeDlsiU7Fw5H6idp0KDY/HdW7+OEajbQtTd76I92JLRTONrKBi2JYzt mJ0NFzpWHWpI+baQ1AmZbP9iikgmI0w= ARC-Authentication-Results: i=1; imf13.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b="l/gkZ57m"; spf=pass (imf13.hostedemail.com: domain of brauner@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=brauner@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1787181094; b=UXY/sA4MhLOtv2+cLglAJQuiv/TStZotZECmky1bBs4uQh54F9UVF0Gwj6fYcrTrSr0XEb A6wqfI2TFphZk34m1tSE9lLN8qKkBc25Eit8QGr5veCq32ujxm6HLWGJR9eg0sGKroQKmg wBVVDptgLtwwtVYzgguBaq+ZQRlF+Qs= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id 5D7B661899; Wed, 19 Aug 2026 23:11:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CF3351F000E9; Wed, 19 Aug 2026 23:11:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787181094; bh=72gFO+JEMFm/mE5KyMl3szngZahRJUcU2+ZTWkuKUzQ=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=l/gkZ57m6x0MVqexlIB/w3JhkEQ/mTP5nyLhU30ic1zHxAyQpA+y+AVskrHJNhiWL SI2jlxBw1EjdpadUcI/2A7P8ClVic3G3yU1pobKVs/z5WXqAjKd4IdFfkSWWCM6h6Q gABt5r1yAPuoRGCmxDtpQ/1Y4zl4lgYSUaQBbpMdeMQiTN/zx4rXCp1j6VuKKU73Go bomiUP0HgV4440yO+vYhzrgBbGT2GMZE+iJhtzEq0RnQoCRguvwdYV2qkC58iZfyZ1 NxsO7LrU+v7+V4jutQEHM5GJ/MMyOXp4cjQg6nVnOrDFHGiB7iIIkE6sktM2WpceL3 Y4sF9a5Hopcog== From: Christian Brauner Date: Thu, 20 Aug 2026 01:09:34 +0200 Subject: [PATCH v2 17/22] coredump: describe the holes when COREDUMP_SPARSE is negotiated MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260820-work-coredump-sparse-v2-17-ba32dd718c51@kernel.org> References: <20260820-work-coredump-sparse-v2-0-ba32dd718c51@kernel.org> In-Reply-To: <20260820-work-coredump-sparse-v2-0-ba32dd718c51@kernel.org> To: linux-fsdevel@vger.kernel.org Cc: Jacob Lalonde , Josef Bacik , Jann Horn , Alexander Viro , Jan Kara , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Omar Sandoval , Jacob Lalonde , Shuah Khan , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, "Christian Brauner (Amutable)" X-Mailer: b4 0.17-dev-362b8 X-Developer-Signature: v=1; a=openpgp-sha256; l=4977; i=brauner@kernel.org; h=from:subject:message-id; bh=SaaeoMeiN9Mzcytct1cOKja7m2Y3FzATAK/meN2hUkQ=; b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWS1me+PdVFZciP6KiOziPLkjCPrt4aY2OkX5d9iajx34 WHpM9v0jlIWBjEuBlkxRRaHdpNwueU8FZuNMjVg5rAygQxh4OIUgInMWM/I8Ko0T+d2zco97zmF vm1mDJ1xNqjz4AbuFR6Feh1RpamLORkZVrqnlC9Qy/36LDrokmhKV7HBSe1XSXxH/U5vuqau7ri UCQA= X-Developer-Key: i=brauner@kernel.org; a=openpgp; fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624 X-Stat-Signature: d4zkrss9t17u6tj4pncfqdmtt1y67sxr X-Rspamd-Queue-Id: B84B72000C X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1787181094-672188 X-HE-Meta: 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 bLsSVwOS N6RSIV8FHgK/wiHl+b/RufgdolZTvysK1bKzz9ON/175+/tRTnH+2IuJ4GD8jXxtBXhL/DgqLc+oTWpcp4aVMpO3TvnQAp5vQW2cjc5nSZr38HVISM1JuGfim0nk+faUDEnsI1nLHVXVPOraT8UI0dSSSkdlm9bsiAh64fXqDYDGtJBgLRnB+bdIb5L1sBkwB4pOm0EAOB81TVtUxn+65jsyuNvBORS6yz5VaSecGGZs1q7+Rv6fKnVnU60mEB9K7lIgSK95ktEBfB3IdZTQiGB5leLIUpLnBiyHn Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Make use of COREDUMP_SPARSE. Refuse it without COREDUMP_RECORDS. Actual holes are sent as a record with length indicating how much zero data there was. coredump_write() flushes a trailing hole if the coredump is done. Instead of writing the actual byte for pipes and sockets, collapse it. This stops wasting a header with coredump records for a single byte. So we now only write it when the coredump can be seeked. TL;DR a trailing hole is a zero record like any other and the records still cover the whole coredump. Signed-off-by: Christian Brauner (Amutable) --- fs/coredump.c | 41 +++++++++++++++++----- .../selftests/coredump/coredump_test_helpers.c | 3 +- 2 files changed, 35 insertions(+), 9 deletions(-) diff --git a/fs/coredump.c b/fs/coredump.c index b1679930094c..7b568d25887c 100644 --- a/fs/coredump.c +++ b/fs/coredump.c @@ -68,6 +68,7 @@ static bool dump_vma_snapshot(struct coredump_params *cprm); static void free_vma_snapshot(struct coredump_params *cprm); static void dump_end_record(struct coredump_params *cprm); +static bool dump_flush_skip(struct coredump_params *cprm); #define CORE_FILE_NOTE_SIZE_DEFAULT (4*1024*1024) /* Define a reasonable max cap */ @@ -806,7 +807,7 @@ static bool coredump_sock_request(struct core_name *cn, struct coredump_params * .size = sizeof(struct coredump_req), .mask = COREDUMP_KERNEL | COREDUMP_USERSPACE | COREDUMP_REJECT | COREDUMP_WAIT | - COREDUMP_RECORDS, + COREDUMP_RECORDS | COREDUMP_SPARSE, .size_ack = sizeof(struct coredump_ack), }; struct coredump_ack ack = {}; @@ -866,6 +867,12 @@ static bool coredump_sock_request(struct core_name *cn, struct coredump_params * return false; } + /* Zero records only exist inside a record stream. */ + if ((ack.mask & COREDUMP_SPARSE) && !(ack.mask & COREDUMP_RECORDS)) { + coredump_sock_mark(cprm->file, COREDUMP_MARK_CONFLICTING); + return false; + } + /* Record header scratch; a bvec can't point at the stack. */ if (ack.mask & COREDUMP_RECORDS) { cprm->record_hdr = kmalloc_obj(*cprm->record_hdr); @@ -1076,15 +1083,21 @@ static bool coredump_write(struct coredump_params *cprm, if (!binfmt->core_dump(cprm)) cprm->state |= COREDUMP_STATE_TRUNCATED; /* - * Ensures that file size is big enough to contain the current - * file position. This prevents gdb from complaining about - * a truncated file if the last "write" to the file was - * dump_skip. A record stream relies on it too: the flush - * emits the records that cover a trailing hole. + * A trailing hole still has to land in the coredump. Seeking over + * it doesn't grow the file, so the last byte of it is written + * instead and gdb doesn't see a truncated file. Everything else + * puts the hole on the wire as it flushes it. */ if (cprm->to_skip) { - cprm->to_skip--; - if (!dump_emit(cprm, "", 1)) + bool flushed; + + if (cprm->file->f_mode & FMODE_LSEEK) { + cprm->to_skip--; + flushed = dump_emit(cprm, "", 1); + } else { + flushed = dump_flush_skip(cprm); + } + if (!flushed) cprm->state |= COREDUMP_STATE_TRUNCATED; } dump_end_record(cprm); @@ -1241,6 +1254,11 @@ static bool dump_records(const struct coredump_params *cprm) return cprm->mask & COREDUMP_RECORDS; } +static bool dump_sparse(const struct coredump_params *cprm) +{ + return cprm->mask & COREDUMP_SPARSE; +} + /* Describe the next @len bytes of the coredump. Returns the header size. */ static size_t dump_record_init(struct coredump_params *cprm, enum coredump_record_type type, u64 flags, @@ -1357,6 +1375,13 @@ static bool __dump_skip(struct coredump_params *cprm, size_t nr) static char zeroes[PAGE_SIZE]; struct file *file = cprm->file; + if (dump_sparse(cprm)) { + /* Hand the server the length of the hole instead of the hole itself. */ + if (dump_interrupted()) + return false; + return dump_emit_record(cprm, COREDUMP_RECORD_ZERO, 0, nr); + } + if (file->f_mode & FMODE_LSEEK) { if (dump_interrupted() || vfs_llseek(file, nr, SEEK_CUR) < 0) return false; diff --git a/tools/testing/selftests/coredump/coredump_test_helpers.c b/tools/testing/selftests/coredump/coredump_test_helpers.c index 1c8658f35735..a5b9cde47239 100644 --- a/tools/testing/selftests/coredump/coredump_test_helpers.c +++ b/tools/testing/selftests/coredump/coredump_test_helpers.c @@ -275,7 +275,8 @@ bool send_coredump_ack(int fd, const struct coredump_req *req, /* Every option the kernel is expected to advertise in coredump_req->mask. */ #define TEST_REQ_MASK_ALL \ (COREDUMP_KERNEL | COREDUMP_USERSPACE | \ - COREDUMP_REJECT | COREDUMP_WAIT | COREDUMP_RECORDS) + COREDUMP_REJECT | COREDUMP_WAIT | \ + COREDUMP_RECORDS | COREDUMP_SPARSE) bool check_coredump_req(const struct coredump_req *req) { -- 2.53.0