Please sign in to comment.
bootmem/sparsemem: remove limit constraint in alloc_bootmem_section
commit f5bf18f upstream. While testing AMS (Active Memory Sharing) / CMO (Cooperative Memory Overcommit) on powerpc, we tripped the following: kernel BUG at mm/bootmem.c:483! cpu 0x0: Vector: 700 (Program Check) at [c000000000c03940] pc: c000000000a62bd8: .alloc_bootmem_core+0x90/0x39c lr: c000000000a64bcc: .sparse_early_usemaps_alloc_node+0x84/0x29c sp: c000000000c03bc0 msr: 8000000000021032 current = 0xc000000000b0cce0 paca = 0xc000000001d80000 pid = 0, comm = swapper kernel BUG at mm/bootmem.c:483! enter ? for help [c000000000c03c80] c000000000a64bcc .sparse_early_usemaps_alloc_node+0x84/0x29c [c000000000c03d50] c000000000a64f10 .sparse_init+0x12c/0x28c [c000000000c03e20] c000000000a474f4 .setup_arch+0x20c/0x294 [c000000000c03ee0] c000000000a4079c .start_kernel+0xb4/0x460 [c000000000c03f90] c000000000009670 .start_here_common+0x1c/0x2c This is BUG_ON(limit && goal + size > limit); and after some debugging, it seems that goal = 0x7ffff000000 limit = 0x80000000000 and sparse_early_usemaps_alloc_node -> sparse_early_usemaps_alloc_pgdat_section calls return alloc_bootmem_section(usemap_size() * count, section_nr); This is on a system with 8TB available via the AMS pool, and as a quirk of AMS in firmware, all of that memory shows up in node 0. So, we end up with an allocation that will fail the goal/limit constraints. In theory, we could "fall-back" to alloc_bootmem_node() in sparse_early_usemaps_alloc_node(), but since we actually have HOTREMOVE defined, we'll BUG_ON() instead. A simple solution appears to be to unconditionally remove the limit condition in alloc_bootmem_section, meaning allocations are allowed to cross section boundaries (necessary for systems of this size). Johannes Weiner pointed out that if alloc_bootmem_section() no longer guarantees section-locality, we need check_usemap_section_nr() to print possible cross-dependencies between node descriptors and the usemaps allocated through it. That makes the two loops in sparse_early_usemaps_alloc_node() identical, so re-factor the code a bit. [email@example.com: code simplification] Signed-off-by: Nishanth Aravamudan <firstname.lastname@example.org> Cc: Dave Hansen <email@example.com> Cc: Anton Blanchard <firstname.lastname@example.org> Cc: Paul Mackerras <email@example.com> Cc: Ben Herrenschmidt <firstname.lastname@example.org> Cc: Robert Jennings <email@example.com> Acked-by: Johannes Weiner <firstname.lastname@example.org> Acked-by: Mel Gorman <email@example.com> Signed-off-by: Andrew Morton <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com> Signed-off-by: Greg Kroah-Hartman <firstname.lastname@example.org>
- Loading branch information...