On Mon, Jul 31, 2023 at 10:12:08PM +0100, Lorenzo Stoakes wrote: > On Mon, Jul 31, 2023 at 10:34:21PM +0200, Jiri Olsa wrote: > > On Mon, Jul 31, 2023 at 08:40:24PM +0100, Lorenzo Stoakes wrote: > > > On Mon, Jul 31, 2023 at 09:24:50PM +0200, David Hildenbrand wrote: > > > > On 31.07.23 21:21, Lorenzo Stoakes wrote: > > > > > On Mon, Jul 24, 2023 at 08:23:55AM +0200, David Hildenbrand wrote: > > > > > > Hi, > > > > > > > > > > > > > > > > > > > > I met this too when I executed below command to trigger a kcore reading. > > > > > > > I wanted to do a simple testing during system running and got this. > > > > > > > > > > > > > > makedumpfile --mem-usage /proc/kcore > > > > > > > > > > > > > > Later I tried your above objdump testing, it corrupted system too. > > > > > > > > > > > > > > > > > > > What do you mean with "corrupted system too" -- did it not only fail to > > > > > > dump the system, but also actually harmed the system? > > > > > > > > > > > > @Lorenzo do you plan on reproduce + fix, or should we consider reverting > > > > > > that change? > > > > > > > > > > > > -- > > > > > > Cheers, > > > > > > > > > > > > David / dhildenb > > > > > > > > > > > > > > > > Apologies I mised this, I have been very busy lately not least with book :) > > > > > > > > > > Concerning, I will take a look as I get a chance. I think the whole series > > > > > would have to be reverted which would be... depressing... as other patches > > > > > in series eliminates the bounce buffer altogether. > > > > > > > > > > > > > I spotted > > > > > > > > https://lkml.kernel.org/r/069dd40aa71e634b414d07039d72467d051fb486.camel@xxxxxx > > > > > > > > > > Find that slightly confusing, they talk about just reveritng the patch but then > > > also add a kern_addr_valid()? > > > > > > I'm also confused about people talking about just reverting the patch, as > > > 4c91c07c93bb drops the bounce buffer altogether... presumably they mean > > > reverting both? > > > > > > Clearly this is an arm64 thing (obviously), I have some arm64 hardware let me > > > see if I can repro... > > > > I see the issue on x86 > > Ummmm what? I can't! What repro are you seeing on x86, exactly? # cat /proc/kallsyms | grep ksys_read ffffffff8151e450 T ksys_read # objdump -d --start-address=0xffffffff8151e450 --stop-address=0xffffffff8151e460 /proc/kcore /proc/kcore: file format elf64-x86-64 objdump: Reading section load1 failed because: Bad address jirka > > > > > > > > > Baoquan, Jiri - are you reverting more than just the one commit? And does doing > > > this go from not working -> working? Or from not working (worst case oops) -> > > > error? > > > > yes, I used to revert all 4 patches > > > > I did quick check and had to revert 2 more patches to get clean revert > > > > 38b138abc355 Revert "fs/proc/kcore: avoid bounce buffer for ktext data" > > e2c3b418d365 Revert "fs/proc/kcore: convert read_kcore() to read_kcore_iter()" > > d8bc432cb314 Revert "iov_iter: add copy_page_to_iter_nofault()" > > bf2c6799f68c Revert "iov_iter: Kill ITER_PIPE" > > ccf4b2c5c5ce Revert "mm: vmalloc: convert vread() to vread_iter()" > > de400d383a7e Revert "mm/vmalloc: replace the ternary conditional operator with min()" > > > > jirka > > That's quite a few more reverts and obviously not an acceptable solution here. > > Looking at > https://lore.kernel.org/all/CAA5enKaUYehLZGL3abv4rsS7caoUG-pN9wF3R+qek-DGNZufbA@xxxxxxxxxxxxxx > a parallel thread on this, it looks like the issue is that we are no longer > using a no-fault kernel copy in KCORE_TEXT path and arm64 doesn't map everything > in the text range. > > Solution would be to reinstate the bounce buffer in this case (ugh). Longer term > solution I think would be to create some iterator helper that does no fault > copies from the kernel. > > I will try to come up with a semi-revert that keeps the iterator stuff but > keeps a hideous bounce buffer for the KCORE_TEXT bit with a comment > explaining why...
