Greetings Pascal, After following the links I see what's happening. Essentially: - Kernel gained RO/RW correctness check - circa Jan 2018, kernel commit 721c7fc701c71f693307d274d2b346a1ecd4a534 - LVM was initially buggy but later fixed, circa Mar 2018, - Kernel check got partially reverted because broken LVM is still used - circa Aug 2018, kernel commit a32e236eb93e62a0f692e79b7c3c9636689559b9 - People used an out of tree patch, reinstating the correctness check - The function return type was dropped since it is unused - Sep 2022, kernel commit bdb7d420c6f6d2618d4c907cd7742c3195c425e2 - kernel patch no longer applies, correct behaviour cannot be enforced To unblock yourself, it will be a matter of reverting bdb7d420c6f6d2618d4c907cd7742c3195c425e2 and then a32e236eb93e62a0f692e79b7c3c9636689559b9. For the mid/long run, one should consider a proper upstream solution: Assuming I'm in your position, I would dig through the data in the linked commits and estimate which/how many distributions ship with buggy LVM. Then formulate a comprehensive cover letter, proposing a) reverts (if LVM is no longer used in the wild) or b) reverts && a (KCONFIG, sysctl, other) toggle to control the behaviour. Hope that helps, Emil On Wed, 15 Mar 2023 at 13:38, Pascal <patatetom@xxxxxxxxx> wrote: > > hi Emil, > > in view of your answer and after rereading my email, I realize that I was confused in my request. > here it is, I hope, more clearly reformulated :-) > > first of all, I use ArchLinux to, from time to time, compile the slightly modified LTS kernel, and this from PKGBUILD provided by ArchLinux at some point. > > some technologies such as LVM do not take into account the read-only applied on a block device. > see the two links provided in the previous exchanges for more details... > > > until now, I recompiled the kernel by applying a slight modification to the bio_check_ro function present in the blk-core.c source file. > the last time I made this modification was on the Linux-LTS-5.10.19 kernel : > (https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/block/blk-core.c?h=v5.10.19) > > $ diff -u 5.10.19.original/blk-core.c 5.10.19.me/blk-core.c > --- 5.10.19.original/blk-core.c 2023-03-15 13:44:20.176929833 +0100 > +++ 5.10.19.me/blk-core.c 2023-03-15 13:44:02.353596114 +0100 > @@ -706,7 +706,7 @@ > "Trying to write to read-only block-device %s (partno %d)\n", > bio_devname(bio, b), part->partno); > /* Older lvm-tools actually trigger this */ > - return false; > + return true; > } > > return false; > > the compilation of the modified LTS 5.10.19 kernel went well and the correction seems to do the job... > > > since this last time (2022/01), the source file blk-core.c has been modified a lot and the bio_check_ro function is part of these modifications : > (https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/block/blk-core.c?h=v6.1.15) > > $ diff -u 5.10.19.original/blk-core.c 6.1.15.original/blk-core.c > --- 5.10.19.original/blk-core.c 2023-03-15 13:44:20.176929833 +0100 > +++ 6.1.15.original/blk-core.c 2023-03-15 13:50:36.560271323 +0100 > @@ -14,11 +14,10 @@ > */ > #include <linux/kernel.h> > #include <linux/module.h> > -#include <linux/backing-dev.h> > #include <linux/bio.h> > #include <linux/blkdev.h> > -#include <linux/blk-mq.h> > ... > @@ -681,40 +483,22 @@ > } > > late_initcall(fail_make_request_debugfs); > - > -#else /* CONFIG_FAIL_MAKE_REQUEST */ > - > -static inline bool should_fail_request(struct hd_struct *part, > - unsigned int bytes) > -{ > - return false; > -} > - > #endif /* CONFIG_FAIL_MAKE_REQUEST */ > > -static inline bool bio_check_ro(struct bio *bio, struct hd_struct *part) > +static inline void bio_check_ro(struct bio *bio) > { > - const int op = bio_op(bio); > - > - if (part->policy && op_is_write(op)) { > - char b[BDEVNAME_SIZE]; > - > + if (op_is_write(bio_op(bio)) && bdev_read_only(bio->bi_bdev)) { > if (op_is_flush(bio->bi_opf) && !bio_sectors(bio)) > - return false; > - > - WARN_ONCE(1, > - "Trying to write to read-only block-device %s (partno %d)\n", > - bio_devname(bio, b), part->partno); > + return; > + pr_warn("Trying to write to read-only block-device %pg\n", > + bio->bi_bdev); > /* Older lvm-tools actually trigger this */ > - return false; > } > - > - return false; > } > ... > > > when I introduce my little modification (see diff below) in the code, makepkg fails to compile with the error "return with a value in function returning void" (see makepkg below) : > > $ diff -u 6.1.15.original/blk-core.c 6.1.15.me/blk-core.c > --- 6.1.15.original/blk-core.c 2023-03-15 13:50:36.560271323 +0100 > +++ 6.1.15.me/blk-core.c 2023-03-15 13:56:15.246945330 +0100 > @@ -493,6 +493,7 @@ > pr_warn("Trying to write to read-only block-device %pg\n", > bio->bi_bdev); > /* Older lvm-tools actually trigger this */ > + return true; > } > } > > $ makepkg > ... > CC block/blk-core.o > block/blk-core.c: In function 'bio_check_ro': > block/blk-core.c:496:24: error: 'return' with a value, in function returning void [-Werror=return-type] > 496 | return true; > | ^~~~ > block/blk-core.c:488:20: note: declared here > 488 | static inline void bio_check_ro(struct bio *bio) > | ^~~~~~~~~~~~ > cc1: some warnings being treated as errors > make[2]: *** [scripts/Makefile.build:250: block/blk-core.o] Error 1 > make[1]: *** [scripts/Makefile.build:500: block] Error 2 > make: *** [Makefile:2005: .] Error 2 > > > so, how to modify the current code of the bio_check_ro function to get the desired result (eg. writes KO on RO blockdevice) ? > with the changes in the blk-core.c source code since version 5.10.19, is it still necessary to tweak the bio_check_ro function to disallow technologies that ignore the read-only block? > > regards, lacsaP. > > Le mer. 15 mars 2023 à 12:37, Emil Velikov <emil.l.velikov@xxxxxxxxx> a écrit : >> >> Greetings Pascal, >> >> Couple of suggestions from the peanut gallery, Take them with a heavy >> pinch of salt: >> - Is the issue happening with upstream code from kernel.org? >> - Consider mentioning the commit sha (and URL, if it is missing from >> kernel.org) in the email >> - Is "intervened" the right word here - the Cambridge dictionary >> defines it as "to intentionally become involved in a difficult >> situation in order to improve it or prevent it from getting worse" >> - Are you contacting a developer only? Have you considered adding the >> subsystem maintainer and mailing list in the CC list - >> scripts/get_maintainer.pl will give you those >> - Have you considered opening a bug report, or better yet sending a >> patch? Patch does not have to be perfect and if you have doubts you >> can mention those in the email/cover-letter. >> >> Hope that helps >> Emil >> >> [1] https://dictionary.cambridge.org/dictionary/english/intervene >> >> On Wed, 15 Mar 2023 at 08:42, Pascal <patatetom@xxxxxxxxx> wrote: >> > >> > hi, >> > >> > I come to you for lack of feedback (I think the Linux kernel developers have other cats to whip :-)) >> > would one of you have the answer or a track to follow concerning the question below ? >> > the encountered compilation error is behind the forwarded email. >> > >> > regards, lacsaP. >> > >> > ---------- Forwarded message --------- >> > De : Pascal <patatetom@xxxxxxxxx> >> > Date: mer. 8 mars 2023 à 14:09 >> > Subject: bio_check_ro @ blk-core.c >> > >> > hi, >> > >> > I'm addressing you because you intervened (commit) in the function bio_check_ro @ blk-core.c @ Linux-LTS-6.1.15. >> > the last time I intervened on this file (@ Linux-LTS-5.10.19 for personal use), it was to replace "return false;" by "return true;", which theoretically should prevent the possible writing on a device locked in read-only mode (see here or here). >> > with @ Linux-LTS-6.1.15, if I insert "return true;", I now have a compilation error. >> > in your opinion, is there still a need to "fix" blk-core.c to prevent writing to a read-only locked device and if so, can you help me implement this fix? >> > >> > regards, lacsaP. >> > ---------- End forwarded message --------- >> > >> > SYNC include/config/auto.conf >> > CC arch/x86/kernel/asm-offsets.s >> > CALL scripts/checksyscalls.sh >> > DESCEND objtool >> > DESCEND bpf/resolve_btfids >> > CC block/bdev.o >> > CC block/fops.o >> > CC block/bio.o >> > CC block/elevator.o >> > CC block/blk-core.o >> > block/blk-core.c: In function 'bio_check_ro': >> > block/blk-core.c:496:24: error: 'return' with a value, in function returning void [-Werror=return-type] >> > 496 | return true; >> > | ^~~~ >> > block/blk-core.c:488:20: note: declared here >> > 488 | static inline void bio_check_ro(struct bio *bio) >> > | ^~~~~~~~~~~~ >> > cc1: some warnings being treated as errors >> > make[2]: *** [scripts/Makefile.build:250: block/blk-core.o] Error 1 >> > make[1]: *** [scripts/Makefile.build:500: block] Error 2 >> > make: *** [Makefile:2005: .] Error 2
