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b=Kf+52144YXxmSkV3VJTo5FiPwLKlB61+gSnUu2Z7QE6c/l8/fQCzrmDuKVV9i5Fgq s5OGA87ZUjhjDC7bEcH5gE/I3eeNatuhLtCGgFWKXKUceu/f/yi8ETT0K7NsE4SXMW J2ArM6yTtHwrx5MrneOrmNqebpb165FfAZz4gjQY8IXLVW0/X8ArNbn2hQGAgixTbX lMFyGbND3NpQZQBZ3MFSPEXxL51e6UEEoJX/oz6fmm4JxN0gI0Evec3ZCp9xM5s+uG SPF6O9RheHzIwSH9VG/sWNzwK32w8FUSNTpJb4TivTSb0yt/ixr+drLbVd6xJ40NT0 CJsG2xyWTwMDw== Message-ID: <9a8e189a-39b4-4571-bdd5-400cf6443204@kernel.org> Date: Thu, 25 Jun 2026 13:43:07 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4] coredump: Add /proc//coredump_pre_exit for pre-exit before dumping To: Pedro Falcato Cc: Christian Brauner , Mike Rapoport , Lorenzo Stoakes , mjguzik@gmail.com, ebiederm@xmission.com, viro@zeniv.linux.org.uk, jack@suse.cz, jlayton@kernel.org, chuck.lever@oracle.com, alex.aring@gmail.com, arnd@arndb.de, keescook@chromium.org, mcgrof@kernel.org, j.granados@samsung.com, allen.lkml@gmail.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Xin Zhao , linux-mm@kvack.org References: <20260624145552.70143-1-jackzxcui1989@163.com> <20260625-wappnen-drohbrief-wermutstropfen-c53538f01547@brauner> <9105c433-44a7-4e8f-bacb-def93d11a7f2@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: kufsfazbc535irakwgon9uktpf37fz7s X-Rspam-User: X-Rspamd-Queue-Id: 2CEBA18000F X-Rspamd-Server: rspam02 X-HE-Tag: 1782387796-772826 X-HE-Meta: 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 8G1yQcYg MkJv4UuvimiyqYr3MsF0/r3PxpWeENaSMw3L9P11qGUBS4soGKcSms9aunwcwoKZ5gtspjvhNwY/7+feDg4Gf7gjlzHKydwJKvUWXxOrx5j0737SMKMGPA4Iugtli4O3JUKjXfLkU8wh3oPFoBp+kdmd0+qm0Gn9p3ZYqRtvqOVWzaAtOmFMycgTkZha0bvT17RD4of+gHW9GmoWeRaUOMPB8sUl3ngx4f0KWOaM6QKeYAO0+XXoB2qMldm/mSMsMbpiUoVrmNREJYrKWmOHRwCsktu+EClV5yOjICsCu9wnNZUv6YpUWCCl7Z6tTxIZU+OQ9VoapkzrNrAKcDkC6QHEA86So1ZjNzLEihOy3F5nJY5itySWy2ez//cgCIm/ufh6P Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/25/26 13:18, Pedro Falcato wrote: > On Thu, Jun 25, 2026 at 12:57:02PM +0200, David Hildenbrand (Arm) wrote: >>> >>> This makes no sense. I think you really need to sit down and think about >>> a design for this that doesn't introduce state machinery for boot, mm, >>> and the VFS in one shot to solve a fringe problem... >> >> Staring at exit_mmap_mapped_shared(), ... this looks rather hacky ("let's fake >> munmap and set some magical flags"). >> >> We're essentially saying "we don't want (pretty much) anything that's MAP_SHARED >> in the coredump". And for some reason someone should configure that, that's a >> rather weird toggle tbh. >> >> And the granularity ("file-backed shared memory") is completely odd. >> >> >> Aren't there other ways we could optimize this internally? >> >> Like, if we know that a process is dead and cannot run anymore, downgrade writes >> to reads (and make sure we block GUP write attempts accordingly), or would that >> also not be sufficient? >> >> >> Another thought: >> >> fs/coredump.c calls get_dump_page(). >> >> get_dump_page() will not fault in any memory. So if a page is not in the page >> tables at the time of the dump, it will not get included in the coredump. Which >> means, that whether most non-anonymous memory will be included in a coredump is >> already like playing the lottery. >> >> This is true for MAP_SHARED file mappings and MAP_PRIVATE file mappings without >> private modifications. >> >> Which makes me wonder: How much is tooling relying on file-backed pages to end >> up in a coredump? > > FWIW this mechanism already exists, see /proc/self/coredump_filter. The > default is bits 0, 1, 4 and 5 (see core(5)), which maps back to no file pages > being dumped to a core dump, apart from ELF headers (these help the debugger > trace back the mapped binary to the debug info using the buildid). > > So the answer to this question is "approximately none" :) > Ah, thanks! vma_dump_size() honors this, and I am sure through some magical routing the information stored in m->dump_size will end up not dumping these pages. Staring at elf_core_dump(), this "unmap some stuff" part is really, really nasty, as it effectively removes the VMAs->segments from the dump. (unless I am missing something important) -- Cheers, David