On 8/28/19 4:00 AM, Michal Hocko wrote: > On Tue 27-08-19 16:22:38, Michal Hocko wrote: >> Dan, isn't this something we have discussed recently? > This was http://lkml.kernel.org/r/20190725023100.31141-3-t-fukasawa@xxxxxxxxxxxxx > and talked about /proc/kpageflags but this is essentially the same thing > AFAIU. I hope we get a consistent solution for both issues. > Yes, it is the same problem. The uninitialized page structure problem affects all the 3 /proc/kpage{cgroup,count,flags) files. Toshiki's patch seems to fix it just for /proc/kpageflags, though. -Longman >> On Mon 26-08-19 08:43:36, Waiman Long wrote: >>> It was found that on a dual-socket x86-64 system with nvdimm, reading >>> /proc/kpagecount may cause the system to panic: >>> >>> =================== >>> [ 79.917682] BUG: unable to handle page fault for address: fffffffffffffffe >>> [ 79.924558] #PF: supervisor read access in kernel mode >>> [ 79.929696] #PF: error_code(0x0000) - not-present page >>> [ 79.934834] PGD 87b60d067 P4D 87b60d067 PUD 87b60f067 PMD 0 >>> [ 79.940494] Oops: 0000 [#1] SMP NOPTI >>> [ 79.944157] CPU: 89 PID: 3455 Comm: cp Not tainted 5.3.0-rc5-test+ #14 >>> [ 79.950682] Hardware name: Dell Inc. PowerEdge R740/07X9K0, BIOS 2.2.11 06/13/2019 >>> [ 79.958246] RIP: 0010:kpagecount_read+0xdb/0x1a0 >>> [ 79.962859] Code: e8 09 83 e0 3f 48 0f a3 02 73 2d 4c 89 f7 48 c1 e7 06 48 03 3d fe da de 00 74 1d 48 8b 57 08 48 8d 42 ff 83 e2 01 48 0f 44 c7 <48> 8b 00 f6 c4 02 75 06 83 7f 30 80 7d 62 31 c0 4c 89 f9 e8 5d c9 >>> [ 79.981603] RSP: 0018:ffffb0d9c950fe70 EFLAGS: 00010202 >>> [ 79.986830] RAX: fffffffffffffffe RBX: ffff8beebe5383c0 RCX: ffffb0d9c950ff00 >>> [ 79.993963] RDX: 0000000000000001 RSI: 00007fd85b29e000 RDI: ffffe77a22000000 >>> [ 80.001095] RBP: 0000000000020000 R08: 0000000000000001 R09: 0000000000000000 >>> [ 80.008226] R10: 0000000000000000 R11: 0000000000000001 R12: 00007fd85b29e000 >>> [ 80.015358] R13: ffffffff893f0480 R14: 0000000000880000 R15: 00007fd85b29e000 >>> [ 80.022491] FS: 00007fd85b312800(0000) GS:ffff8c359fb00000(0000) knlGS:0000000000000000 >>> [ 80.030576] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >>> [ 80.036321] CR2: fffffffffffffffe CR3: 0000004f54a38001 CR4: 00000000007606e0 >>> [ 80.043455] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >>> [ 80.050586] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 >>> [ 80.057718] PKRU: 55555554 >>> [ 80.060428] Call Trace: >>> [ 80.062877] proc_reg_read+0x39/0x60 >>> [ 80.066459] vfs_read+0x91/0x140 >>> [ 80.069686] ksys_read+0x59/0xd0 >>> [ 80.072922] do_syscall_64+0x59/0x1e0 >>> [ 80.076588] entry_SYSCALL_64_after_hwframe+0x44/0xa9 >>> [ 80.081637] RIP: 0033:0x7fd85a7f5d75 >>> =================== >>> >>> It turns out the panic was caused by the kpagecount_read() function >>> hitting an uninitialized page structure at PFN 0x880000 where all its >>> fields were set to -1. The compound_head value of -1 will mislead the >>> kernel to treat -2 as a pointer to the head page of the compound page >>> leading to the crash. >>> >>> The system have 12 GB of nvdimm ranging from PFN 0x880000-0xb7ffff. >>> However, only PFN 0x88c200-0xb7ffff are released by the nvdimm >>> driver to the kernel and initialized. IOW, PFN 0x880000-0x88c1ff >>> remain uninitialized. Perhaps these 196 MB of nvdimm are reserved for >>> internal use. >>> >>> To fix the panic, we need to find out if a page structure has been >>> initialized. This is done now by checking if the PFN is in the range >>> of a memory zone assuming that pages in a zone is either correctly >>> marked as not present in the mem_section structure or have their page >>> structures initialized. >>> >>> Signed-off-by: Waiman Long <longman@xxxxxxxxxx> >>> --- >>> fs/proc/page.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++--- >>> 1 file changed, 65 insertions(+), 3 deletions(-) >>> >>> diff --git a/fs/proc/page.c b/fs/proc/page.c >>> index 544d1ee15aee..fee55ad95893 100644 >>> --- a/fs/proc/page.c >>> +++ b/fs/proc/page.c >>> @@ -21,6 +21,64 @@ >>> #define KPMMASK (KPMSIZE - 1) >>> #define KPMBITS (KPMSIZE * BITS_PER_BYTE) >>> >>> +/* >>> + * It is possible a page structure is contained in a mem_section that is >>> + * regarded as valid but the page structure itself is not properly >>> + * initialized. For example, portion of the device memory may be used >>> + * internally by device driver or firmware without being managed by the >>> + * kernel and hence their page structures may not be initialized. >>> + * >>> + * An uninitialized page structure may cause the PFN iteration code >>> + * in this file to panic the system. To safe-guard against this >>> + * possibility, an additional check of the PFN is done to make sure >>> + * that it is in a valid range in one of the memory zones: >>> + * >>> + * [zone_start_pfn, zone_start_pfn + spanned_pages) >>> + * >>> + * It is possible that some of the PFNs within a zone is not present. >>> + * In this case, it will have to rely on the current mem_section check >>> + * as well as the affected page structures are still properly initialized. >>> + */ >>> +struct zone_range { >>> + unsigned long pfn_start; >>> + unsigned long pfn_end; >>> +}; >>> + >>> +static void find_next_zone_range(struct zone_range *range) >>> +{ >>> + unsigned long start, end; >>> + pg_data_t *pgdat; >>> + struct zone *zone; >>> + int i; >>> + >>> + /* >>> + * Scan all the zone structures to find the next closest one. >>> + */ >>> + start = end = -1UL; >>> + for (pgdat = first_online_pgdat(); pgdat; >>> + pgdat = next_online_pgdat(pgdat)) { >>> + for (zone = pgdat->node_zones, i = 0; i < MAX_NR_ZONES; >>> + zone++, i++) { >>> + if (!zone->spanned_pages) >>> + continue; >>> + if ((zone->zone_start_pfn >= range->pfn_end) && >>> + (zone->zone_start_pfn < start)) { >>> + start = zone->zone_start_pfn; >>> + end = start + zone->spanned_pages; >>> + } >>> + } >>> + } >>> + range->pfn_start = start; >>> + range->pfn_end = end; >>> +} >>> + >>> +static inline bool pfn_in_zone(unsigned long pfn, struct zone_range *range) >>> +{ >>> + if (pfn >= range->pfn_end) >>> + find_next_zone_range(range); >>> + return pfn >= range->pfn_start && pfn < range->pfn_end; >>> +} >>> + >>> /* /proc/kpagecount - an array exposing page counts >>> * >>> * Each entry is a u64 representing the corresponding >>> @@ -31,6 +89,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, >>> { >>> u64 __user *out = (u64 __user *)buf; >>> struct page *ppage; >>> + struct zone_range range = { 0, 0 }; >>> unsigned long src = *ppos; >>> unsigned long pfn; >>> ssize_t ret = 0; >>> @@ -42,10 +101,11 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, >>> return -EINVAL; >>> >>> while (count > 0) { >>> - if (pfn_valid(pfn)) >>> + if (pfn_valid(pfn) && pfn_in_zone(pfn, &range)) >>> ppage = pfn_to_page(pfn); >>> else >>> ppage = NULL; >>> + >>> if (!ppage || PageSlab(ppage) || page_has_type(ppage)) >>> pcount = 0; >>> else >>> @@ -206,6 +266,7 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf, >>> { >>> u64 __user *out = (u64 __user *)buf; >>> struct page *ppage; >>> + struct zone_range range = { 0, 0 }; >>> unsigned long src = *ppos; >>> unsigned long pfn; >>> ssize_t ret = 0; >>> @@ -216,7 +277,7 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf, >>> return -EINVAL; >>> >>> while (count > 0) { >>> - if (pfn_valid(pfn)) >>> + if (pfn_valid(pfn) && pfn_in_zone(pfn, &range)) >>> ppage = pfn_to_page(pfn); >>> else >>> ppage = NULL; >>> @@ -250,6 +311,7 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf, >>> { >>> u64 __user *out = (u64 __user *)buf; >>> struct page *ppage; >>> + struct zone_range range = { 0, 0 }; >>> unsigned long src = *ppos; >>> unsigned long pfn; >>> ssize_t ret = 0; >>> @@ -261,7 +323,7 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf, >>> return -EINVAL; >>> >>> while (count > 0) { >>> - if (pfn_valid(pfn)) >>> + if (pfn_valid(pfn) && pfn_in_zone(pfn, &range)) >>> ppage = pfn_to_page(pfn); >>> else >>> ppage = NULL; >>> -- >>> 2.18.1 >> -- >> Michal Hocko >> SUSE Labs
