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authorYongseok Koh <yongseok.koh@samsung.com>2010-01-19 17:33:49 +0900
committerLinus Torvalds <torvalds@linux-foundation.org>2010-01-21 07:20:06 -0800
commit88f5004430babb836cfce886d5d54c82166f8ba4 (patch)
treef1cdd2f63e6344a07a3470f6cd4face94da3e638
parent970114a1dacf5f1f47aae9ad75c0abca42d8499c (diff)
downloadlinux-88f5004430babb836cfce886d5d54c82166f8ba4.tar.gz
vmalloc: remove BUG_ON due to racy counting of VM_LAZY_FREE
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 [ See also http://marc.info/?l=linux-kernel&m=126335856228090&w=2 ] Signed-off-by: Yongseok Koh <yongseok.koh@samsung.com> Reviewed-by: Minchan Kim <minchan.kim@gmail.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/vmalloc.c4
1 files changed, 1 insertions, 3 deletions
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 37e69295f25..d55d905463e 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -555,10 +555,8 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end,
}
rcu_read_unlock();
- if (nr) {
- BUG_ON(nr > atomic_read(&vmap_lazy_nr));
+ if (nr)
atomic_sub(nr, &vmap_lazy_nr);
- }
if (nr || force_flush)
flush_tlb_kernel_range(*start, *end);