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linux/mm
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Linus Torvalds 4542057e18 mm: avoid 'might_sleep()' in get_mmap_lock_carefully() 
This might_sleep() goes back a long time: it was originally introduced
way back when by commit 010060741a ("x86: add might_sleep() to
do_page_fault()"), and made it into the generic VM code when the x86
fault path got re-organized and generalized in commit c2508ec5a5 ("mm:
introduce new 'lock_mm_and_find_vma()' page fault helper").

However, it turns out that the placement of that might_sleep() has
always been rather questionable simply because it's not only a debug
statement to warn about sleeping in contexts that shouldn't sleep (which
was the original reason for adding it), but it also implies a voluntary
scheduling point.

That, in turn, is less than desirable for two reasons:

 (a) it ends up being done after we successfully got the mmap_lock, so
     just as we got the lock we will now eagerly schedule away and
     increase lock contention

and

 (b) this is all very possibly part of the "oops, things went horribly
     wrong" path and we just haven't figured that out yet

After all, the whole _reason_ for having that get_mmap_lock_carefully()
rather than just doing the obvious mmap_read_lock() is because this code
wants to deal somewhat gracefully with potential kernel wild pointer
bugs.

So then a voluntary scheduling point here is simply not a good idea.

We could certainly turn the 'might_sleep()' into a '__might_sleep()' and
make it be just the debug check that it was originally intended to be.

But even that seems questionable in the wild kernel pointer case - which
again is part of the whole point of this code.  The problem wouldn't be
about the _sleeping_ part of the page fault, but about a bad kernel
access.  The fact that that bad kernel access might happen in a section
that you shouldn't sleep in is secondary.

So it really ends up being the case that this is simply entirely the
wrong place to do this debug check and related scheduling point at all.

So let's just remove the check entirely.  It's been around for over a
decade, it has served its purpose.

The re-schedule will happen at return to user space anyway for the
normal case, and the warning - if we even need it - might be better off
done as a special case for "page fault from kernel mode" once we've
dealt with any potential kernel oopses where the oops is the relevant
thing, not some artificial "scheduling while atomic" test.

Reported-by: Mateusz Guzik <mjguzik@gmail.com>
Link: https://lore.kernel.org/lkml/20230820104303.2083444-1-mjguzik@gmail.com/
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2023-08-21 06:11:33 +02:00
..
damon mm/damon/core: initialize damo_filter->list from damos_new_filter() 2023-08-04 13:03:43 -07:00
kasan kasan, slub: fix HW_TAGS zeroing with slub_debug 2023-07-08 09:29:32 -07:00
kfence mm/slab: introduce kmem_cache flag SLAB_NO_MERGE 2023-06-02 10:24:33 +02:00
kmsan kasan,kmsan: remove __GFP_KSWAPD_RECLAIM usage from kasan/kmsan 2023-06-23 16:59:26 -07:00
backing-dev.c mm: backing-dev: make bdi_class a static const structure 2023-06-23 16:59:27 -07:00
balloon_compaction.c
bootmem_info.c
cma.c mm/page_owner/cma: show pfn in cma/page_owner with hex format 2023-06-19 16:19:32 -07:00
cma.h
cma_debug.c mm/cma_debug: show complete cma name in debugfs directories 2022-09-11 20:25:50 -07:00
cma_sysfs.c mm: cma: make kobj_type structure constant 2023-03-28 16:20:06 -07:00
compaction.c mm: compaction: fix endless looping over same migrate block 2023-08-04 13:03:42 -07:00
debug.c mm: update validate_mm() to use vma iterator 2023-06-09 16:25:31 -07:00
debug_page_alloc.c mm: page_alloc: split out DEBUG_PAGEALLOC 2023-06-09 16:25:23 -07:00
debug_page_ref.c
debug_vm_pgtable.c mm/debug_vm_pgtable,page_table_check: warn pte map fails 2023-06-19 16:19:15 -07:00
dmapool.c dmapool: create/destroy cleanup 2023-06-09 16:25:17 -07:00
dmapool_test.c dmapool: add alloc/free performance test 2023-04-05 19:42:38 -07:00
early_ioremap.c mm/early_ioremap.c: improve the execution efficiency of early_ioremap_setup() 2023-06-09 16:25:56 -07:00
fadvise.c mm: remove unnecessary pagevec includes 2023-06-23 16:59:31 -07:00
fail_page_alloc.c mm: page_alloc: split out FAIL_PAGE_ALLOC 2023-06-09 16:25:23 -07:00
failslab.c mm: fix unexpected changes to {failslab|fail_page_alloc}.attr 2022-11-22 18:50:44 -08:00
filemap.c - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
folio-compat.c - Nick Piggin's "shoot lazy tlbs" series, to improve the peformance of 2023-04-27 19:42:02 -07:00
frontswap.c mm: zswap: support exclusive loads 2023-06-19 16:19:05 -07:00
gup.c gup: make the stack expansion warning a bit more targeted 2023-07-05 09:33:31 -07:00
gup_test.c Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-06-23 16:58:19 -07:00
gup_test.h mm/gup_test: start/stop/read functionality for PIN LONGTERM test 2022-11-08 17:37:15 -08:00
highmem.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
hmm.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
huge_memory.c mm: remove references to pagevec 2023-06-23 16:59:30 -07:00
hugetlb.c hugetlb: do not clear hugetlb dtor until allocating vmemmap 2023-08-04 13:03:41 -07:00
hugetlb_cgroup.c mm/hugetlb: increase use of folios in alloc_huge_page() 2023-02-13 15:54:27 -08:00
hugetlb_vmemmap.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
hugetlb_vmemmap.h
hwpoison-inject.c mm/hwpoison: add __init/__exit annotations to module init/exit funcs 2022-10-03 14:03:05 -07:00
init-mm.c IOMMU Updates for Linux 6.4 2023-04-30 13:00:38 -07:00
internal.h - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
interval_tree.c
io-mapping.c
ioremap.c
Kconfig mm: disable CONFIG_PER_VMA_LOCK until its fixed 2023-07-08 09:29:29 -07:00
Kconfig.debug mm: page_table_check: Make it dependent on EXCLUSIVE_SYSTEM_RAM 2023-05-29 16:14:28 +01:00
khugepaged.c mm/khugepaged: fix regression in collapse_file() 2023-06-29 09:41:45 -07:00
kmemleak.c lib/stackdepot, mm: rename stack_depot_want_early_init 2023-02-16 20:43:49 -08:00
ksm.c mm/swapfile: fix wrong swap entry type for hwpoisoned swapcache page 2023-08-04 13:03:40 -07:00
list_lru.c
maccess.c mm: Fix copy_from_user_nofault(). 2023-04-12 17:36:23 -07:00
madvise.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
Makefile mm: page_alloc: split out DEBUG_PAGEALLOC 2023-06-09 16:25:23 -07:00
mapping_dirty_helpers.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
memblock.c Revert "mm,memblock: reset memblock.reserved to system init state to prevent UAF" 2023-07-28 09:47:06 -07:00
memcontrol.c mm/memcontrol: do not tweak node in mem_cgroup_init() 2023-06-23 16:59:26 -07:00
memfd.c memfd: check for non-NULL file_seals in memfd_create() syscall 2023-06-19 13:19:31 -07:00
memory-failure.c mm: memory-failure: avoid false hwpoison page mapped error info 2023-08-04 13:03:41 -07:00
memory-tiers.c memory tier: remove unneeded !IS_ENABLED(CONFIG_MIGRATION) check 2023-06-19 16:19:29 -07:00
memory.c mm: avoid 'might_sleep()' in get_mmap_lock_carefully() 2023-08-21 06:11:33 +02:00
memory_hotplug.c mm: remove unnecessary pagevec includes 2023-06-23 16:59:31 -07:00
mempolicy.c mm/mempolicy: Take VMA lock before replacing policy 2023-07-28 09:44:06 -07:00
mempool.c mempool: do not use ksize() for poisoning 2022-11-30 15:58:41 -08:00
memremap.c mm/memremap.c: fix outdated comment in devm_memremap_pages 2023-02-09 16:51:46 -08:00
memtest.c mm/memtest: add results of early memtest to /proc/meminfo 2023-04-05 19:42:55 -07:00
migrate.c mm: remove unnecessary pagevec includes 2023-06-23 16:59:31 -07:00
migrate_device.c mm: remove references to pagevec 2023-06-23 16:59:30 -07:00
mincore.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
mlock.c mm/mlock: fix vma iterator conversion of apply_vma_lock_flags() 2023-07-17 12:53:21 -07:00
mm_init.c - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
mm_slot.h mm: introduce common struct mm_slot 2022-10-03 14:02:43 -07:00
mmap.c mm: lock VMA in dup_anon_vma() before setting ->anon_vma 2023-07-27 13:07:04 -07:00
mmap_lock.c
mmu_gather.c mm: prefer xxx_page() alloc/free functions for order-0 pages 2023-03-28 16:20:16 -07:00
mmu_notifier.c mm/mmu_notifier: remove unused mmu_notifier_range_update_to_read_only export 2023-02-02 22:32:54 -08:00
mmzone.c mm: multi-gen LRU: groundwork 2022-09-26 19:46:09 -07:00
mprotect.c Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-06-23 16:58:19 -07:00
mremap.c mm: Update do_vmi_align_munmap() return semantics 2023-07-01 08:10:56 -07:00
msync.c mm/msync: use vma_find() instead of vma linked list 2022-09-26 19:46:25 -07:00
nommu.c xtensa: fix lock_mm_and_find_vma in case VMA not found 2023-07-01 08:00:05 -07:00
oom_kill.c mm, oom: do not check 0 mask in out_of_memory() 2023-06-09 16:25:20 -07:00
page-writeback.c writeback: account the number of pages written back 2023-07-08 09:29:30 -07:00
page_alloc.c - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
page_counter.c mm: page_counter: remove unneeded atomic ops for low/min 2022-09-11 20:26:01 -07:00
page_ext.c mm/page_ext: init page_ext early if there are no deferred struct pages 2023-02-02 22:33:22 -08:00
page_idle.c mm: page_idle: convert page idle to use a folio 2023-01-18 17:12:52 -08:00
page_io.c swap: use __bio_add_page to add page to bio 2023-05-31 09:50:02 -06:00
page_isolation.c mm: page_isolation: write proper kerneldoc 2023-06-19 16:18:59 -07:00
page_owner.c mm/page_owner/cma: show pfn in cma/page_owner with hex format 2023-06-19 16:19:32 -07:00
page_poison.c
page_reporting.c mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
page_reporting.h
page_table_check.c - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
page_vma_mapped.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
pagewalk.c mm/pagewalk: fix EFI_PGT_DUMP of espfix area 2023-07-27 13:07:04 -07:00
percpu-internal.h percpu-internal/pcpu_chunk: re-layout pcpu_chunk structure to reduce false sharing 2023-06-19 16:19:29 -07:00
percpu-km.c
percpu-stats.c
percpu-vm.c
percpu.c mm: memcontrol: rename memcg_kmem_enabled() 2023-02-16 20:43:56 -08:00
pgalloc-track.h
pgtable-generic.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
process_vm_access.c mm/gup: remove unused vmas parameter from pin_user_pages_remote() 2023-06-09 16:25:25 -07:00
ptdump.c mm: ptdump should use ptep_get_lockless() 2023-06-19 16:19:24 -07:00
readahead.c mm: remove unnecessary pagevec includes 2023-06-23 16:59:31 -07:00
rmap.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
rodata_test.c mm/rodata_test: use PAGE_ALIGNED() helper 2022-10-03 14:03:05 -07:00
secretmem.c mm/mlock: rename mlock_future_check() to mlock_future_ok() 2023-06-09 16:25:38 -07:00
shmem.c shmem: minor fixes to splice-read implementation 2023-07-27 13:07:03 -07:00
show_mem.c mm: page_alloc: collect mem statistic into show_mem.c 2023-06-09 16:25:22 -07:00
shrinker_debug.c Revert "mm: shrinkers: make count and scan in shrinker debugfs lockless" 2023-06-19 13:19:34 -07:00
shuffle.c mm/shuffle: convert module_param_call to module_param_cb 2022-10-03 14:03:07 -07:00
shuffle.h mm, treewide: redefine MAX_ORDER sanely 2023-04-05 19:42:46 -07:00
slab.c slab updates for 6.5 2023-06-29 16:34:12 -07:00
slab.h kasan, slub: fix HW_TAGS zeroing with slub_debug 2023-07-08 09:29:32 -07:00
slab_common.c slab updates for 6.5 2023-06-29 16:34:12 -07:00
slub.c slab updates for 6.5 2023-06-29 16:34:12 -07:00
sparse-vmemmap.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
sparse.c - Arnd Bergmann has fixed a bunch of -Wmissing-prototypes in 2023-06-28 10:59:38 -07:00
swap.c mm: remove references to pagevec 2023-06-23 16:59:30 -07:00
swap.h mm: remove the __swap_writepage return value 2023-02-02 22:33:33 -08:00
swap_cgroup.c mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled 2022-10-03 14:03:36 -07:00
swap_slots.c mm/swap: convert put_swap_page() to put_swap_folio() 2022-10-03 14:02:46 -07:00
swap_state.c mm: remove unnecessary pagevec includes 2023-06-23 16:59:31 -07:00
swapfile.c mm/swapfile: fix wrong swap entry type for hwpoisoned swapcache page 2023-08-04 13:03:40 -07:00
truncate.c mm: remove references to pagevec 2023-06-23 16:59:30 -07:00
usercopy.c mm: Fix copy_from_user_nofault(). 2023-04-12 17:36:23 -07:00
userfaultfd.c mm: ptep_get() conversion 2023-06-19 16:19:25 -07:00
util.c mm: uninline kstrdup() 2023-04-08 13:45:37 -07:00
vmalloc.c Merge mm-hotfixes-stable into mm-stable to pick up depended-upon changes. 2023-06-23 16:58:19 -07:00
vmpressure.c
vmscan.c mm/vmscan: fix root proactive reclaim unthrottling unbalanced node 2023-06-23 16:59:32 -07:00
vmstat.c - Yosry Ahmed brought back some cgroup v1 stats in OOM logs. 2023-06-28 10:28:11 -07:00
workingset.c Multi-gen LRU: fix workingset accounting 2023-06-09 16:25:46 -07:00
z3fold.c mm: zswap: remove shrink from zpool interface 2023-06-19 16:19:27 -07:00
zbud.c mm: zswap: remove shrink from zpool interface 2023-06-19 16:19:27 -07:00
zpool.c mm: zswap: remove shrink from zpool interface 2023-06-19 16:19:27 -07:00
zsmalloc.c zsmalloc: fix races between modifications of fullness and isolated 2023-08-04 13:03:40 -07:00
zswap.c mm: zswap: fix double invalidate with exclusive loads 2023-06-23 16:59:31 -07:00