Re: [PATCH v1] kernel/module: allocate module vmap space after making sure the module is unique

Miroslav Benes
2022-10-14T06:09:47Z

Hi,

On Thu, 13 Oct 2022, David Hildenbrand wrote:

> We already make sure to allocate percpu data only after we verified that
> the module we're loading hasn't already been loaded and isn't
> concurrently getting loaded -- that it's unique.
>
> On big systems (> 400 CPUs and many devices) with KASAN enabled, we're now
> phasing a similar issue with the module vmap space.
>
> When KASAN_INLINE is enabled (resulting in large module size), plenty
> of devices that udev wants to probe and plenty (> 400) of CPUs that can
> carry out that probing concurrently, we can actually run out of module
> vmap space and trigger vmap allocation errors:
>
> [ 165.818200] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.836622] vmap allocation for size 315392 failed: use vmalloc=<size> to increase size
> [ 165.837461] vmap allocation for size 315392 failed: use vmalloc=<size> to increase size
> [ 165.840573] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.841059] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.841428] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.841819] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.842123] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.843359] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.844894] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
> [ 165.847028] CPU: 253 PID: 4995 Comm: systemd-udevd Not tainted 5.19.0 #2
> [ 165.935689] Hardware name: Lenovo ThinkSystem SR950 -[7X12ABC1WW]-/-[7X12ABC1WW]-, BIOS -[PSE130O-1.81]- 05/20/2020
> [ 165.947343] Call Trace:
> [ 165.950075] <TASK>
> [ 165.952425] dump_stack_lvl+0x57/0x81
> [ 165.956532] warn_alloc.cold+0x95/0x18a
> [ 165.960836] ? zone_watermark_ok_safe+0x240/0x240
> [ 165.966100] ? slab_free_freelist_hook+0x11d/0x1d0
> [ 165.971461] ? __get_vm_area_node+0x2af/0x360
> [ 165.976341] ? __get_vm_area_node+0x2af/0x360
> [ 165.981219] __vmalloc_node_range+0x291/0x560
> [ 165.986087] ? __mutex_unlock_slowpath+0x161/0x5e0
> [ 165.991447] ? move_module+0x4c/0x630
> [ 165.995547] ? vfree_atomic+0xa0/0xa0
> [ 165.999647] ? move_module+0x4c/0x630
> [ 166.003741] module_alloc+0xe7/0x170
> [ 166.007747] ? move_module+0x4c/0x630
> [ 166.011840] move_module+0x4c/0x630
> [ 166.015751] layout_and_allocate+0x32c/0x560
> [ 166.020519] load_module+0x8e0/0x25c0
> [ 166.024623] ? layout_and_allocate+0x560/0x560
> [ 166.029586] ? kernel_read_file+0x286/0x6b0
> [ 166.034269] ? __x64_sys_fspick+0x290/0x290
> [ 166.038946] ? userfaultfd_unmap_prep+0x430/0x430
> [ 166.044203] ? lock_downgrade+0x130/0x130
> [ 166.048698] ? __do_sys_finit_module+0x11a/0x1c0
> [ 166.053854] __do_sys_finit_module+0x11a/0x1c0
> [ 166.058818] ? __ia32_sys_init_module+0xa0/0xa0
> [ 166.063882] ? __seccomp_filter+0x92/0x930
> [ 166.068494] do_syscall_64+0x59/0x90
> [ 166.072492] ? do_syscall_64+0x69/0x90
> [ 166.076679] ? do_syscall_64+0x69/0x90
> [ 166.080864] ? do_syscall_64+0x69/0x90
> [ 166.085047] ? asm_sysvec_apic_timer_interrupt+0x16/0x20
> [ 166.090984] ? lockdep_hardirqs_on+0x79/0x100
> [ 166.095855] entry_SYSCALL_64_after_hwframe+0x63/0xcd[ 165.818200] vmap allocation for size 2498560 failed: use vmalloc=<size> to increase size
>
> Interestingly, when reducing the number of CPUs (nosmt), it works as
> expected.
>
> The underlying issue is that we first allocate memory (including module
> vmap space) in layout_and_allocate(), and then verify whether the module
> is unique in add_unformed_module(). So we end up allocating module vmap
> space even though we might not need it -- which is a problem when modules
> are big and we can have a lot of concurrent probing of the same set of
> modules as on the big system at hand.
>
> Unfortunately, we cannot simply add the module earlier, because
> move_module() -- that allocates the module vmap space -- essentially
> brings the module to life from a temporary one. Adding the temporary one
> and replacing it is also sub-optimal (because replacing it would require
> to synchronize against RCU) and feels kind of dangerous judging that we
> end up copying it.
>
> So instead, add a second list (pending_load_infos) that tracks the modules
> (via their load_info) that are unique and are still getting loaded
> ("pending"), but haven't made it to the actual module list yet. This
> shouldn't have a notable runtime overhead when concurrently loading
> modules: the new list is expected to usually either be empty or contain
> very few entries for a short time.
>
> Thanks to Uladzislau for his help to verify that it's not actually a
> vmap code issue.

this seems to be related to what
https://lore.kernel.org/all/20220919123233.8538-1-petr.pavlu@suse.com/
tries to solve. Just your symptoms are different. Does the patch set fix
your issue too?

Regards
Miroslav