From: Theodore Ts'o Subject: Re: [RFC PATCH] coredump: avoid ext4 auto_da_alloc for core file Date: Tue, 5 Jul 2016 12:57:15 -0400 Message-ID: <20160705165715.GH15193@thunk.org> References: <5cdda475417b2719dced162cce89a283153cb818.1466012020.git.osandov@fb.com> <20160705143714.GG15193@thunk.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Omar Sandoval , Al Viro , linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, kernel-team@fb.com To: Josef Bacik Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Tue, Jul 05, 2016 at 11:01:40AM -0400, Josef Bacik wrote: > > > Omar, this probably breaks the case where we do > > > fallocate(FALLOC_FL_KEEP_SIZE), the i_size will be 0 but there will be > > > blocks to truncate. Probably want to check i_blocks or something. Thanks, > > > > Sure, but this is in the coredump code; do we care there? What are > > the odds that someone will have fallocated blocks beyond i_size in a > > file named "core"? And if so, it's not like it's going to make the > > coredump invalid or non-useful in any way. > > Wow I totally didn't notice this was in coredump.c, I thought it was in ext4 > code because you said it failed regression tests, which I assumed were your > ext4 tests. Ignore me. Thanks, Yeah, Omar's original patch was something he described as a "hack" to the coredump code. I actually don't think it's that bad, but it does make sense to have ext4 not enable the "replace-via-truncate" code when the truncate is a no-op, but it turns out this is a bit tricky because the places where we set i_size and where we decide to truncate beyond i_size are separated. I tried to do something simple but it didn't quite work right; I'll look into why it didn't work hopefully later today. - Ted