I ran into an overflow problem in the module tag area. With profiling toggled off, the overflow check in reserve_module_tags() did not run, a module could load with more tags than the page flags can address, and re-enabling profiling then silently corrupted /proc/allocinfo. On overflow the fix shuts profiling down, releases the reservation and returns -EAGAIN, and the codetag section lands as regular module data in the same load, so the module loads without profiling.
Review of the earlier series by Sashiko turned up two more problems. One is a race. layout_sections() and move_module() both asked codetag_needs_module_section() where a codetag section goes, and mem_profiling_support can change between the two calls, for instance when another module load overflows the tag index and shuts profiling down. move_module() then copied the codetag section to offset 0 of its regular destination and clobbered the first section placed in that region. v7 reworks where codetag sections are allocated, on a prototype by Petr Pavlu [1]. The allocation runs before layout_sections() and the placement is decided in one step, so nothing re-asks the question and the race is gone. The retry is gone too, on -EAGAIN the section is laid out as regular module data right in the same load. [1] https://lore.kernel.org/all/[email protected]/ Following review feedback from Petr and Suren the series is now split into four patches. Patch 1 moves release_module_tags() above reserve_module_tags(), since the failure paths now have to call it. Patch 2 cleans up the populate failure path: the reservation is released, module_tags.size rolled back and the PTEs a failed vmap_pages_range() left behind unmapped, so a later populate of the same range is safe. It carries both Fixes tags so it backports wherever patch 4 goes, which uses its prev_size. Patch 3 introduces SH_ENTSIZE_STANDALONE to mark sections with a separate allocation, per the ELF spec SHF_ALLOC means a section occupies memory during execution, and the percpu section does, only outside the regular module layout. It was previously excluded from the layout by clearing its SHF_ALLOC, overloading the flag with a loader-internal meaning. The mark lives in sh_entsize now, find_sec(".data..percpu") gives stable results again and apply_relocations() goes back to testing only SHF_ALLOC. The section would now show up under /sys/module/*/sections/, but it has one instance per CPU and no single address to report, and the entry never existed before, so add_sect_attrs() and add_notes_attrs() skip it. Patch 4 moves the codetag allocation out of move_module() in front of layout_sections(). On overflow reserve_module_tags() shuts profiling down, releases the reservation, rolls module_tags.size back and returns -EAGAIN, and the section is laid out as regular module data, so the module loads without profiling instead of failing. Any other error fails the load. The release and the fallback belong together, without the release rmmod hits the stale entry and panics. Tested on an x86_64 virtual machine: Booted without sysctl.vm.mem_profiling=1,compressed: # cat /proc/allocinfo is fine Booted with sysctl.vm.mem_profiling=1,compressed: # cat /proc/allocinfo is fine # insmod overflow_tag.ko # dmesg With module overflow_tag there are too many tags to fit in 13 page flag bits. Memory allocation profiling is disabled! # rmmod overflow_tag The module loads without profiling and unloads cleanly. Changes in v9: - do not export .data..percpu under /sys/module/*/sections/ (Petr Pavlu). - move the populate failure cleanup in front of the rework, v8 patch 4 is patch 2 now. It declares prev_size itself, which the overflow path of the rework also uses, so it carries both Fixes tags and the two patches backport together Changes in v8: - roll back module_tags.size when the reservation is released, so a concurrent load which already passed needs_section_mem() does not skip populate for the freed gap (Sashiko) - unmap the PTEs a failed vmap_pages_range() installed, a retry to populate the same range would BUG on them - zero the separately allocated codetag memory for an SHT_NOBITS section, the tag area pages are not zeroed on allocation (Sashiko) - .data..percpu is exported under /sys/module/*/sections/ with the boot CPU instance of the per-cpu area, and the interface is documented in the ABI docs (Petr Pavlu) - keep a comment in apply_relocations() on how .data..percpu is relocated (Petr Pavlu) - replace the "Based-on-a-patch-by:" tag with an in-body attribution and a numbered Link: (Andrew Morton) Changes in v7: - split the rework following review feedback (Petr Pavlu, Suren Baghdasaryan) - new patch 2 marks separately allocated sections with SH_ENTSIZE_STANDALONE instead of clearing SHF_ALLOC (suggested by Petr Pavlu) - split the populate failure release into its own patch (suggested by Suren Baghdasaryan) Changes in v6: - rework on Petr's prototype and allocate codetag sections before layout_sections(), the retry and its state resets are gone - fix the layout_sections()/move_module() race (Found by Sashiko) - release the reservation on populate failure as well (Found by Sashiko) - only -EAGAIN keeps the fallback, other errors fail the load Changes in v5: - add Fixes: and Cc: stable to patch 1/2 as well, since 2/2 does not compile without it (Andrew Morton) - restore frob-adjusted mem[type].size on retry instead of zeroing, as s390 and parisc add GOT/PLT space there in module_frob_arch_sections() (Reported by Sashiko) - drop the load_module() mem_profiling_support check; the percpu counter leak is pre-existing and orthogonal to this fix Changes in v4: - add a new patch (1/2) to move release_module_tags() above reserve_module_tags(); the overflow fix is 2/2 - release the reservation on the -EAGAIN path - return -EAGAIN instead of -ENOMEM so the module can still load without profiling (Suren) - reset sh_addr, mem[type].size and sym/str SHF_ALLOC before retry - skip percpu counters in load_module() when profiling is off Changes in v3: - use pr_warn_once() instead of pr_warn() - return -ENOMEM instead of -ENOSPC (Suren) - expand the commit message to describe the /proc/allocinfo impact (Andrew) Changes in v2: - return an error after shutdown_mem_profiling() to skip vm_module_tags_populate() v1: https://lore.kernel.org/all/[email protected]/ v2: https://lore.kernel.org/all/[email protected]/ v3: https://lore.kernel.org/all/[email protected]/ v4: https://lore.kernel.org/all/[email protected]/ v5: https://lore.kernel.org/all/[email protected]/ v6: https://lore.kernel.org/all/[email protected]/ v7: https://lore.kernel.org/all/[email protected]/ v8: https://lore.kernel.org/all/[email protected]/ Hao Ge (4): alloc_tag: move release_module_tags() above reserve_module_tags() alloc_tag: clean up the populate failure path module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections module: allocate codetag sections before the regular module layout include/linux/module.h | 2 + kernel/module/internal.h | 8 +++ kernel/module/kallsyms.c | 13 +--- kernel/module/main.c | 133 +++++++++++++++++++++------------------ kernel/module/sysfs.c | 15 ++++- mm/alloc_tag.c | 111 +++++++++++++++++--------------- 6 files changed, 158 insertions(+), 124 deletions(-) -- 2.25.1
