Messages in this thread | | | Subject | Re: [PATCH] vmalloc: remove BUG_ON due to racy counting of VM_LAZY_FREE | From | Minchan Kim <> | Date | Tue, 19 Jan 2010 21:01:27 +0900 |
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On Tue, 2010-01-19 at 17:33 +0900, Yongseok Koh wrote: > From: Yongseok Koh <yongseok.koh@samsung.com>
You don't need above line. We use "From" when we send patch instead of someone.
> > In free_unmap_area_noflush(), va->flags is marked as VM_LAZY_FREE first, and > then vmap_lazy_nr is increased atomically. > But, in __purge_vmap_area_lazy(), while traversing of vmap_are_list, nr is > counted by checking VM_LAZY_FREE is set to va->flags. > After counting the variable nr, kernel reads vmap_lazy_nr atomically and > checks a BUG_ON condition whether nr is greater than vmap_lazy_nr to prevent > vmap_lazy_nr from being negative. > > The problem is that, if interrupted right after marking VM_LAZY_FREE, > increment of vmap_lazy_nr can be delayed. > Consequently, BUG_ON condition can be met because nr is counted more than > vmap_lazy_nr. > > It is highly probable when vmalloc/vfree are called frequently. > This scenario have been verified by adding delay between marking > VM_LAZY_FREE and increasing vmap_lazy_nr in free_unmap_area_noflush(). > > Even the vmap_lazy_nr is for checking high watermark, it never be the strict > watermark. > Although the BUG_ON condition is to prevent vmap_lazy_nr from being > negative, vmap_lazy_nr is signed variable. > So, it could go down to negative value temporarily. > > Consequently, removing the BUG_ON condition is proper. > > A possible BUG_ON message is like the below. > > kernel BUG at mm/vmalloc.c:517! > invalid opcode: 0000 [#1] SMP > EIP: 0060:[<c04824a4>] EFLAGS: 00010297 CPU: 3 > EIP is at __purge_vmap_area_lazy+0x144/0x150 > EAX: ee8a8818 EBX: c08e77d4 ECX: e7c7ae40 EDX: c08e77ec > ESI: 000081fe EDI: e7c7ae60 EBP: e7c7ae64 ESP: e7c7ae3c > DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 > Call Trace: > [<c0482ad9>] free_unmap_vmap_area_noflush+0x69/0x70 > [<c0482b02>] remove_vm_area+0x22/0x70 > [<c0482c15>] __vunmap+0x45/0xe0 > [<c04831ec>] vmalloc+0x2c/0x30 > Code: 8d 59 e0 eb 04 66 90 89 cb 89 d0 e8 87 fe ff ff 8b 43 20 89 da 8d 48 > e0 8d 43 20 3b 04 24 75 e7 fe 05 a8 a5 a3 c0 e9 78 ff ff ff <0f> 0b eb fe 90 > 8d b4 26 00 00 00 00 56 89 c6 b8 ac a5 a3 c0 31 > EIP: [<c04824a4>] __purge_vmap_area_lazy+0x144/0x150 SS:ESP 0068:e7c7ae3c > > > Signed-off-by: Yongseok Koh <yongseok.koh@samsung.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
We discussed about this following as. http://marc.info/?l=linux-kernel&m=126335856228090&w=2
Thanks for contribution for linux kernel, Yongseok. :)
-- Kind regards, Minchan Kim
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