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From: Shakeel Butt To: Matthew Wilcox Cc: Andrew Morton , Andrii Nakryiko , Shaurya Rane , "Darrick J . Wong" , Christoph Hellwig , Alexei Starovoitov , Daniel Borkmann , Meta kernel team , bpf@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+09b7d050e4806540153d@syzkaller.appspotmail.com, Christoph Hellwig Subject: Re: [PATCH bpf v2] lib/buildid: use __kernel_read() for sleepable context Message-ID: <3lf3ed3xn2oaenvlqjmypuewtm6gakzbecc7kgqsadggyvdtkr@uyw4boj6igqu> References: <20251218205505.2415840-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: AE4F8100002 X-Rspamd-Server: rspam10 X-Stat-Signature: ko1r4737uui84ihwnfpf84uagqsj6f9p X-HE-Tag: 1766103407-873500 X-HE-Meta: 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 x5KF4GL8 f9AT8ICuzaT3I5vm1d0pxqjvDXEEMLhieKmMnKpG6pZ3rUAp/5XGhiKMrZsxx3JTC0qgOevct6X4OB0FAt1RVlAhR8kA24tVGJNKQHfxttZWX3rfP40O8n2TL+q12c7LAn0zix9w5D6aYYL6mi2lQbF0tlidDGhnK13stHnY9MnigosNj/cl/679jqEY/ovXIE8iUMIyHj65krqMyYg7lROEfGGfpUr9abG3/t9lPLUJ8n9AJ6XEp8ETcbNGNXO7tfjYS2MFx4vB3wAHSTi+ZE6soOZUzot9bsezLofIuc5BkdMHHyY/2IKNzCrT+YUu2II2iUiacNpPDFEM62mYXl3vXCCoDSeunwV8/ogPnhhNDlVNd/gPSJ6d/vg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Dec 18, 2025 at 11:55:39PM +0000, Matthew Wilcox wrote: > On Thu, Dec 18, 2025 at 12:55:05PM -0800, Shakeel Butt wrote: > > + do { > > + ret = __kernel_read(r->file, buf, sz, &pos); > > + if (ret <= 0) { > > + r->err = ret ?: -EIO; > > + return NULL; > > + } > > + buf += ret; > > + sz -= ret; > > + } while (sz > 0); > > Why are you doing a loop around __kernel_read()? eg kernel_read() does > not do a read around __kernel_read(). The callers of kernel_read() > don't do a loop either. So what makes you think it needs to have a loop > around it? I am assuming that __kernel_read() can return less data than the requested. Is that assumption incorrect?