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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 References: <20260820-work-coredump-sparse-v2-0-ba32dd718c51@kernel.org> <20260820-work-coredump-sparse-v2-11-ba32dd718c51@kernel.org> Content-Language: en-US From: R Nageswara Sastry In-Reply-To: <20260820-work-coredump-sparse-v2-11-ba32dd718c51@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: 3nsD3dyD9YpDNwrNy79mh4k3ZJgZAoAH X-Proofpoint-GUID: 5Ftz_v8DnqJwrQicAaxaxCLwd-1LE4ML X-Authority-Analysis: v=2.4 cv=DbEnbPtW c=1 sm=1 tr=0 ts=6aa182b0 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=uNwIYxRw8H9XJLvQjW8A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA5MDE3MyBTYWx0ZWRfX63FEwKXn2pEz lbN9cHVZiZXHc6txdAexnXMJtgrSfc5kgQl/RQL8aZJ3oiw7NqTF/WCwpFMjKmwq5NLNAZGgf7Q Hos7o2aQf/uCGOISPuipeIO0MunRkNE9zvUd5wusnjKNruB11Hx/j+gFzlJp3hJieicpYa+eeNs VkPI2SMmIPn7I8IL8WFtQVjvsWoy1UeU+NFUVDQ9KSshErJfbe9cDG4v706+PSGMOWzSjuy2imC 9rWzGxzVCn+WakqwhrsdV1oF+VDabMe2ZSGc8J+rU+SeWGZOzqQ4nHzexEQxcNU7ZreEcsXHjqT vnXmtYO1/SidK4tC78nZhlCXtSFAnu9ZuG6T+KEDlEJGJ1VsWRB5SVXl0be+AWY/znuXep8HXml ttmhJajuNA1n59oxzUkxRDb3KE0j9eapA5s1nPeKFV5w3rVkfbJFceEiLji4I9KbtpKV+mI6BiC 6wZ/lWkQABb3bef66Dw== X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA5MDE3MyBTYWx0ZWRfXxpDMqZtbveKw EOHJ1ijEo1wcbWvww4tsJatXr/zaCikRtHGXSA8SYhI/DW4OjGh4H87T7udcjzwwogzipPCpPGc TkIi4XOACd8bpzimfR/h+x2eYMoJeMY= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-08_03,2026-09-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 impostorscore=0 adultscore=0 spamscore=0 clxscore=1015 suspectscore=0 bulkscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609090173 On 20.08.2026 4:39 AM, Christian Brauner wrote: > Right now dump_emit() is the only coredump helper that writes buffers > larger than a page in one call. For elf notes that can easily blow past > PAGE_SIZE. That's annoying because neither pipes nor af_unix sockets > take such writes in one piece. > > If a signal arrives while the writer is waiting they drop a short write. > With the coredump records work coming up that means header and its data > are desynchronized. A write that fits in one pipe buffer or one skb > doesn't suffer from this. > > So split all writes up, including elf notes, and cap every write at a > page. The coredump socket already raises sk_sndbuf far enough for a page > to fit a single skb and pipes always work that way. > > That means dump_interrupted() is now checked once per page. So a large > coredump stops earlier (good). An empty write no longer issues a > zero-length write. The rlimit core check stays where it was. It > continues refusing whole writes. > > Signed-off-by: Christian Brauner (Amutable) Tested-by: R Nageswara Sastry System: ppc64le LPAR (IBM POWER), Linux 7.3-rc2 > --- > fs/coredump.c | 37 ++++++++++++++++++++++++++++++------- > 1 file changed, 30 insertions(+), 7 deletions(-) > > diff --git a/fs/coredump.c b/fs/coredump.c > index d837819031ff..d61f36239f91 100644 > --- a/fs/coredump.c > +++ b/fs/coredump.c > @@ -1215,19 +1215,21 @@ void vfs_coredump(const kernel_siginfo_t *siginfo) > * do on a core-file: use only these functions to write out all the > * necessary info. > */ > -static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) > +/* One write, never more than a page. See __dump_emit(). */ > +static bool dump_emit_chunk(struct coredump_params *cprm, const void *addr, > + int nr) > { > struct file *file = cprm->file; > loff_t pos = file->f_pos; > ssize_t n; > > - if (cprm->written + nr > cprm->limit) > - return false; > if (dump_interrupted()) > return false; > + > n = __kernel_write(file, addr, nr, &pos); > if (n != nr) > return false; > + > file->f_pos = pos; > cprm->written += n; > cprm->pos += n; > @@ -1235,6 +1237,24 @@ static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) > return true; > } > > +static bool __dump_emit(struct coredump_params *cprm, const void *addr, int nr) > +{ > + if (cprm->written + nr > cprm->limit) > + return false; > + > + while (nr) { > + int chunk = min_t(int, nr, PAGE_SIZE); > + > + if (!dump_emit_chunk(cprm, addr, chunk)) > + return false; > + > + addr += chunk; > + nr -= chunk; > + } > + > + return true; > +} > + > static bool __dump_skip(struct coredump_params *cprm, size_t nr) > { > static char zeroes[PAGE_SIZE]; > @@ -1247,13 +1267,16 @@ static bool __dump_skip(struct coredump_params *cprm, size_t nr) > return true; > } > > - while (nr > PAGE_SIZE) { > - if (!__dump_emit(cprm, zeroes, PAGE_SIZE)) > + while (nr) { > + size_t chunk = min_t(size_t, nr, PAGE_SIZE); > + > + if (!__dump_emit(cprm, zeroes, chunk)) > return false; > - nr -= PAGE_SIZE; > + > + nr -= chunk; > } > > - return __dump_emit(cprm, zeroes, nr); > + return true; > } > > /* Flush the accumulated hole before writing data. */ > -- Thanks and Regards R.Nageswara Sastry