On Tue, Jul 20, 2021 at 08:45:45PM -0400, Joshua Kinard wrote: Hi, > (resend using the correct list address) > > Hi all, > > I think there may be an issue with upstream commit > ed914d48b6a1040d1039d371b56273d422c0081e (MIPS: add PMD table accounting > into MIPS'pmd_alloc_one), which got backported to 5.4 LTS. > > I am running my SGI Octane on the 5.4 LTS kernel series w/ Gentoo's IP30 > patches, since basic IP30 support didn't get fully mainlined until ~5.7 and > I am just behind on kernels for the time being. Generally, the 5.4 series > is stable on this machine, but as of using 5.4.133 yesterday and 5.4.134 > today, I have had three kernel panics, all with completely different stack > traces, while building a multilib-enabled glibc-2.33 package. > > Since the stack traces are all completely different, I am suspecting an > issue with memory allocation, which picking through the 5.4.133 changelog, > got me to look at commit ed914d48b6a1. My initial thought is it looks like > this patch should not have been backported to 5.4, because 5.4 is missing > the asm-generic version of pmd_free(), which means the MIPS-specific version > is likely used instead, and that function was not updated alongside > pmd_alloc_one(). > > Now, I am not a memory person, but some quick reading indicates there may be > some other issues with this patch as well: > > - use of 'GFP_KERNEL | __GFP_ACCOUNT' when there is GFP_KERNEL_ACCOUNT > available. Yes, this is better > > - the return value of pgtable_pmd_page_ctor(pg); is not checked to make sure > it succeeded. Per Documentation/vm/split_page_table_lock, "NOTE: > pgtable_page_ctor() and pgtable_pmd_page_ctor() can fail -- it must > be handled properly." Yes, I missed this one > > - there is no call to pgtable_pmd_page_dtor() in pmd_free() in MIPS' > pgalloc. The commit message indicates that pmd_free in asm-generic will > handle this, but that function doesn't exist in 5.4, leading to mismatched > implementations. Yes, my fix is to fix the mismatch. I think all stable branches before 5.10 should *not* apply this my patch > > I think the fix is to either revert ed914d48b6a1 on the 5.4 stable series > (and any earlier series that are missing asm-generic pmd_free), or the MIPS > pmd_free() needs to be updated to call pgtable_pmd_page_dtor() in a similar > manner to x86 and arm64. I'd opt for reverting. > > Currently testing a build of 5.4.134 with this patch reverted running some > compile jobs. If it survives building multilib glibc, then I think my > suspicions may be valid. > > -- > Joshua Kinard > Gentoo/MIPS > kumba@xxxxxxxxxx > rsa6144/5C63F4E3F5C6C943 2015-04-27 > 177C 1972 1FB8 F254 BAD0 3E72 5C63 F4E3 F5C6 C943 > > "The past tempts us, the present confuses us, the future frightens us. And > our lives slip away, moment by moment, lost in that vast, terrible in-between." > > --Emperor Turhan, Centauri Republic
