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? > > > > > 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...
