On Wed, Oct 28, 2020 at 12:17:35PM +0100, David Hildenbrand wrote: > On 28.10.20 12:09, Mike Rapoport wrote: > > On Tue, Oct 27, 2020 at 09:46:35AM +0100, David Hildenbrand wrote: > > > On 27.10.20 09:38, Mike Rapoport wrote: > > > > On Mon, Oct 26, 2020 at 06:05:30PM +0000, Edgecombe, Rick P wrote: > > > > > > > > > Beyond whatever you are seeing, for the latter case of new things > > > > > getting introduced to an interface with hidden dependencies... Another > > > > > edge case could be a new caller to set_memory_np() could result in > > > > > large NP pages. None of the callers today should cause this AFAICT, but > > > > > it's not great to rely on the callers to know these details. > > > > > > A caller of set_memory_*() or set_direct_map_*() should expect a failure > > > > and be ready for that. So adding a WARN to safe_copy_page() is the first > > > > step in that direction :) > > > > > > > > > > I am probably missing something important, but why are we saving/restoring > > > the content of pages that were explicitly removed from the identity mapping > > > such that nobody will access them? > > > > Actually, we should not be saving/restoring free pages during > > hibernation as there are several calls to mark_free_pages() that should > > exclude the free pages from the snapshot. I've tried to find why the fix > > that maps/unmaps a page to save it was required at the first place, but > > I could not find bug reports. > > > > The closest I've got is an email from Rafael that asked to update > > "hibernate: handle DEBUG_PAGEALLOC" patch: > > > > https://lore.kernel.org/linux-pm/200802200133.44098.rjw@xxxxxxx/ > > > > Could it be that safe_copy_page() tries to workaround a non-existent > > problem? > > > > Clould be! Also see > > https://lkml.kernel.org/r/38de5bb0-5559-d069-0ce0-daec66ef2746@xxxxxxx > > which restores free page content based on more kernel parameters, not based > on the original content. Ah, after looking at it now I've run kernel with DEBUG_PAGEALLOC=y and CONFIG_INIT_ON_FREE_DEFAULT_ON=y and restore crahsed nicely. [ 27.210093] PM: Image successfully loaded [ 27.226709] Disabling non-boot CPUs ... [ 27.231208] smpboot: CPU 1 is now offline [ 27.363926] kvm-clock: cpu 0, msr 5c889001, primary cpu clock, resume [ 27.363995] BUG: unable to handle page fault for address: ffff9f7a40108000 [ 27.367996] #PF: supervisor write access in kernel mode [ 27.369558] #PF: error_code(0x0002) - not-present page [ 27.371098] PGD 5ca01067 P4D 5ca01067 PUD 5ca02067 PMD 5ca03067 PTE 800ffffff fef7060 [ 27.373421] Oops: 0002 [#1] SMP DEBUG_PAGEALLOC PTI [ 27.374905] CPU: 0 PID: 1200 Comm: bash Not tainted 5.10.0-rc1 #5 [ 27.376700] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14 .0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 [ 27.379879] RIP: 0010:clear_page_rep+0x7/0x10 [ 27.381218] Code: e8 be 88 75 00 44 89 e2 48 89 ee 48 89 df e8 60 ff ff ff c6 03 00 5b 5d 41 5c c3 cc cc cc cc cc cc cc cc b9 00 02 00 00 31 c0 <f3> 48 ab c3 0f 1f 44 00 00 31 c0 b9 40 00 00 00 66 0f 1f 84 00 00 [ 27.386457] RSP: 0018:ffffb6838046be08 EFLAGS: 00010046 [ 27.388011] RAX: 0000000000000000 RBX: ffff9f7a487c0ec0 RCX: 0000000000000200 [ 27.390082] RDX: ffff9f7a4c788000 RSI: 0000000000000000 RDI: ffff9f7a40108000 [ 27.392138] RBP: ffffffff8629c860 R08: 0000000000000000 R09: 0000000000000007 [ 27.394205] R10: 0000000000000004 R11: ffffb6838046bbf8 R12: 0000000000000000 [ 27.396271] R13: ffff9f7a419a62a0 R14: 0000000000000005 R15: ffff9f7a484f4da0 [ 27.398334] FS: 00007fe0c3f6a700(0000) GS:ffff9f7abf800000(0000) knlGS:0000000000000000 [ 27.400717] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 27.402432] CR2: ffff9f7a40108000 CR3: 000000000859a001 CR4: 0000000000060ef0 [ 27.404485] Call Trace: [ 27.405326] clear_free_pages+0xf5/0x150 [ 27.406568] hibernation_snapshot+0x390/0x3d0 [ 27.407908] hibernate+0xdb/0x240 [ 27.408978] state_store+0xd7/0xe0 [ 27.410078] kernfs_fop_write+0x10e/0x1a0 [ 27.411333] vfs_write+0xbb/0x210 [ 27.412423] ksys_write+0x9c/0xd0 [ 27.413488] do_syscall_64+0x33/0x40 [ 27.414636] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 27.416150] RIP: 0033:0x7fe0c364e380 66 0f 1f 44 00 00 83 3d c9 23 2d 00 00 75 10 b8 01 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 31 c3 48 83 ec 08 e8 fe dd 01 00 48 89 04 24 [ 27.422500] RSP: 002b:00007ffeb64bd0c8 EFLAGS: 00000246 ORIG_RAX: 00000000000 00001 [ 27.424724] RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 00007fe0c364e380 [ 27.426761] RDX: 0000000000000005 RSI: 0000000001eb6408 RDI: 0000000000000001 [ 27.428791] RBP: 0000000001eb6408 R08: 00007fe0c391d780 R09: 00007fe0c3f6a700 [ 27.430863] R10: 0000000000000004 R11: 0000000000000246 R12: 0000000000000005 [ 27.432920] R13: 0000000000000001 R14: 00007fe0c391c620 R15: 0000000000000000 [ 27.434989] Modules linked in: [ 27.436004] CR2: ffff9f7a40108000 [ 27.437075] ---[ end trace 424c466bcd2bfcad ]--- > -- > Thanks, > > David / dhildenb > -- Sincerely yours, Mike.
