hi Emil, forgive me if this is the third time I've replied to this message but I received a moderation warning the two previous times that my reply was over 40Kb when my preparation file was only 13Kb...
I haven't had any feedback about this moderation since last week, so I don't know if you received my answer... this one concluded that the recent version of LVM integrated in the ISO image of ArchLinux modifies a disk, even if this one and all its partitions are set as read-only (chmod 444 /dev/sdX* && blockdev --setro /dev/sdX* with udev rule). thank you for this investigation, this history. regards; lacsaP. Le mer. 15 mars 2023 à 16:36, Emil Velikov <emil.l.veli...@gmail.com> a écrit : > 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 <patate...@gmail.com> 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.veli...@gmail.com> 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 <patate...@gmail.com> 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 <patate...@gmail.com> > >> > 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 >
