linux/mm/debug.c, branch v5.0

mm/debug.c: fix __dump_page() for poisoned pages

2019-02-21T17:01:00Z

Evaluating page_mapping() on a poisoned page ends up dereferencing junk and making PF_POISONED_CHECK() considerably crashier than intended: Unable to handle kernel NULL pointer dereference at virtual address 0000000000000006 Mem abort info: ESR = 0x96000005 Exception class = DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000005 CM = 0, WnR = 0 user pgtable: 4k pages, 39-bit VAs, pgdp = 00000000c2f6ac38 [0000000000000006] pgd=0000000000000000, pud=0000000000000000 Internal error: Oops: 96000005 [#1] PREEMPT SMP Modules linked in: CPU: 2 PID: 491 Comm: bash Not tainted 5.0.0-rc1+ #1 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Dec 17 2018 pstate: 00000005 (nzcv daif -PAN -UAO) pc : page_mapping+0x18/0x118 lr : __dump_page+0x1c/0x398 Process bash (pid: 491, stack limit = 0x000000004ebd4ecd) Call trace: page_mapping+0x18/0x118 __dump_page+0x1c/0x398 dump_page+0xc/0x18 remove_store+0xbc/0x120 dev_attr_store+0x18/0x28 sysfs_kf_write+0x40/0x50 kernfs_fop_write+0x130/0x1d8 __vfs_write+0x30/0x180 vfs_write+0xb4/0x1a0 ksys_write+0x60/0xd0 __arm64_sys_write+0x18/0x20 el0_svc_common+0x94/0xf8 el0_svc_handler+0x68/0x70 el0_svc+0x8/0xc Code: f9400401 d1000422 f240003f 9a801040 (f9400402) ---[ end trace cdb5eb5bf435cecb ]--- Fix that by not inspecting the mapping until we've determined that it's likely to be valid. Now the above condition still ends up stopping the kernel, but in the correct manner: page:ffffffbf20000000 is uninitialized and poisoned raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) ------------[ cut here ]------------ kernel BUG at ./include/linux/mm.h:1006! Internal error: Oops - BUG: 0 [#1] PREEMPT SMP Modules linked in: CPU: 1 PID: 483 Comm: bash Not tainted 5.0.0-rc1+ #3 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Dec 17 2018 pstate: 40000005 (nZcv daif -PAN -UAO) pc : remove_store+0xbc/0x120 lr : remove_store+0xbc/0x120 ... Link: http://lkml.kernel.org/r/03b53ee9d7e76cda4b9b5e1e31eea080db033396.1550071778.git.robin.murphy@arm.com Fixes: 1c6fb1d89e73 ("mm: print more information about mapping in __dump_page") Signed-off-by: Robin Murphy Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/debug.c: make "migrate_reason_names[]" const char *

2018-12-28T20:11:48Z

Those strings are immutable as well. Link: http://lkml.kernel.org/r/20181124090508.GB10877@avx2 Signed-off-by: Alexey Dobriyan Reviewed-by: Andrew Morton Reviewed-by: David Hildenbrand Acked-by: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: lower the printk loglevel for __dump_page messages

2018-12-28T20:11:46Z

__dump_page messages use KERN_EMERG resp. KERN_ALERT loglevel (this is the case since 2004). Most callers of this function are really detecting a critical page state and BUG right after. On the other hand the function is called also from contexts which just want to inform about the page state and those would rather not disrupt logs that much (e.g. some systems route these messages to the normal console). Reduce the loglevel to KERN_WARNING to make dump_page easier to reuse for other contexts while those messages will still make it to the kernel log in most setups. Even if the loglevel setup filters warnings away those paths that are really critical already print the more targeted error or panic and that should make it to the kernel log. [mhocko@kernel.org: fix __dump_page()] Link: http://lkml.kernel.org/r/20181212142540.GA7378@dhcp22.suse.cz [akpm@linux-foundation.org: s/KERN_WARN/KERN_WARNING/, per Michal] Link: http://lkml.kernel.org/r/20181107101830.17405-3-mhocko@kernel.org Signed-off-by: Michal Hocko Reviewed-by: Andrew Morton Reviewed-by: Anshuman Khandual Cc: Baoquan He Cc: Oscar Salvador Cc: Oscar Salvador Cc: William Kucharski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: print more information about mapping in __dump_page

2018-12-28T20:11:46Z

I have been promissing to improve memory offlining failures debugging for quite some time. As things stand now we get only very limited information in the kernel log when the offlining fails. It is usually only [ 1984.506184] rac1 kernel: memory offlining [mem 0x82600000000-0x8267fffffff] failed with no further details. We do not know what exactly fails and for what reason. Whenever I was forced to debug such a failure I've always had to do a debugging patch to tell me more. We can enable some tracepoints but it would be much better to get a better picture without using them. This patch series does 2 things. The first one is to make dump_page more usable by printing more information about the mapping patch 1. Then it reduces the log level from emerg to warning so that this function is usable from less critical context patch 2. Then I have added more detailed information about the offlining failure patch 4 and finally add dump_page to isolation and offlining migration paths. Patch 3 is a trivial cleanup. This patch (of 6): __dump_page prints the mapping pointer but that is quite unhelpful for many reports because the pointer itself only helps to distinguish anon/ksm mappings from other ones (because of lowest bits set). Sometimes it would be much more helpful to know what kind of mapping that is actually and if we know this is a file mapping then also try to resolve the dentry name. [dan.carpenter@oracle.com: fix a width vs precision bug in printk] Link: http://lkml.kernel.org/r/20181123072135.gqvblm2vdujbvfjs@kili.mountain [mhocko@kernel.org: use %dp to print dentry] Link: http://lkml.kernel.org/r/20181125080834.GB12455@dhcp22.suse.cz Link: http://lkml.kernel.org/r/20181107101830.17405-2-mhocko@kernel.org Signed-off-by: Michal Hocko Reviewed-by: Andrew Morton Reviewed-by: Anshuman Khandual Reviewed-by: William Kucharski Cc: Oscar Salvador Cc: Baoquan He Cc: Oscar Salvador Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: provide kernel parameter to allow disabling page init poisoning

2018-10-26T23:26:34Z

Patch series "Address issues slowing persistent memory initialization", v5. The main thing this patch set achieves is that it allows us to initialize each node worth of persistent memory independently. As a result we reduce page init time by about 2 minutes because instead of taking 30 to 40 seconds per node and going through each node one at a time, we process all 4 nodes in parallel in the case of a 12TB persistent memory setup spread evenly over 4 nodes. This patch (of 3): On systems with a large amount of memory it can take a significant amount of time to initialize all of the page structs with the PAGE_POISON_PATTERN value. I have seen it take over 2 minutes to initialize a system with over 12TB of RAM. In order to work around the issue I had to disable CONFIG_DEBUG_VM and then the boot time returned to something much more reasonable as the arch_add_memory call completed in milliseconds versus seconds. However in doing that I had to disable all of the other VM debugging on the system. In order to work around a kernel that might have CONFIG_DEBUG_VM enabled on a system that has a large amount of memory I have added a new kernel parameter named "vm_debug" that can be set to "-" in order to disable it. Link: http://lkml.kernel.org/r/20180925201921.3576.84239.stgit@localhost.localdomain Reviewed-by: Pavel Tatashin Signed-off-by: Alexander Duyck Cc: Dave Hansen Cc: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: get rid of vmacache_flush_all() entirely

2018-09-14T01:18:04Z

Jann Horn points out that the vmacache_flush_all() function is not only potentially expensive, it's buggy too. It also happens to be entirely unnecessary, because the sequence number overflow case can be avoided by simply making the sequence number be 64-bit. That doesn't even grow the data structures in question, because the other adjacent fields are already 64-bit. So simplify the whole thing by just making the sequence number overflow case go away entirely, which gets rid of all the complications and makes the code faster too. Win-win. [ Oleg Nesterov points out that the VMACACHE_FULL_FLUSHES statistics also just goes away entirely with this ] Reported-by: Jann Horn Suggested-by: Will Deacon Acked-by: Davidlohr Bueso Cc: Oleg Nesterov Cc: stable@kernel.org Signed-off-by: Linus Torvalds

mm: teach dump_page() to correctly output poisoned struct pages

2018-07-04T00:32:19Z

If struct page is poisoned, and uninitialized access is detected via PF_POISONED_CHECK(page) dump_page() is called to output the page. But, the dump_page() itself accesses struct page to determine how to print it, and therefore gets into a recursive loop. For example: dump_page() __dump_page() PageSlab(page) PF_POISONED_CHECK(page) VM_BUG_ON_PGFLAGS(PagePoisoned(page), page) dump_page() recursion loop. Link: http://lkml.kernel.org/r/20180702180536.2552-1-pasha.tatashin@oracle.com Fixes: f165b378bbdf ("mm: uninitialized struct page poisoning sanity checking") Signed-off-by: Pavel Tatashin Acked-by: Michal Hocko Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/debug.c: provide useful debugging information for VM_BUG

2018-01-05T00:45:09Z

With the recent addition of hashed kernel pointers, places which need to produce useful debug output have to specify %px, not %p. This patch fixes all the VM debug to use %px. This is appropriate because it's debug output that the user should never be able to trigger, and kernel developers need to see the actual pointers. Link: http://lkml.kernel.org/r/20171219133236.GE13680@bombadil.infradead.org Signed-off-by: Matthew Wilcox Acked-by: Michal Hocko Cc: "Tobin C. Harding" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: consolidate page table accounting

2017-11-16T02:21:04Z

Currently, we account page tables separately for each page table level, but that's redundant -- we only make use of total memory allocated to page tables for oom_badness calculation. We also provide the information to userspace, but it has dubious value there too. This patch switches page table accounting to single counter. mm->pgtables_bytes is now used to account all page table levels. We use bytes, because page table size for different levels of page table tree may be different. The change has user-visible effect: we don't have VmPMD and VmPUD reported in /proc/[pid]/status. Not sure if anybody uses them. (As alternative, we can always report 0 kB for them.) OOM-killer report is also slightly changed: we now report pgtables_bytes instead of nr_ptes, nr_pmd, nr_puds. Apart from reducing number of counters per-mm, the benefit is that we now calculate oom_badness() more correctly for machines which have different size of page tables depending on level or where page tables are less than a page in size. The only downside can be debuggability because we do not know which page table level could leak. But I do not remember many bugs that would be caught by separate counters so I wouldn't lose sleep over this. [akpm@linux-foundation.org: fix mm/huge_memory.c] Link: http://lkml.kernel.org/r/20171006100651.44742-2-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Acked-by: Michal Hocko [kirill.shutemov@linux.intel.com: fix build] Link: http://lkml.kernel.org/r/20171016150113.ikfxy3e7zzfvsr4w@black.fi.intel.com Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm: introduce wrappers to access mm->nr_ptes

2017-11-16T02:21:04Z

Let's add wrappers for ->nr_ptes with the same interface as for nr_pmd and nr_pud. The patch also makes nr_ptes accounting dependent onto CONFIG_MMU. Page table accounting doesn't make sense if you don't have page tables. It's preparation for consolidation of page-table counters in mm_struct. Link: http://lkml.kernel.org/r/20171006100651.44742-1-kirill.shutemov@linux.intel.com Signed-off-by: Kirill A. Shutemov Acked-by: Michal Hocko Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds