> > According to > > https://btrfs.wiki.kernel.org/index.php/Debugging_Btrfs_with_GDB > > UML did work once. > > > > Now it corrupts data and triggers BUG_ON once you > > start to use it. I tried both 2.6.38 and 2.6.39-rc2 (x86_64) > > I need some help to track it down. > > > > doing 'touch `seq 1 11`; rm 11' kills the kernel: > > 2.6.36 works 2.6.37 doesn't. bsecting
Bisected down to:
commit 59daa706fbec745684702741b9f5373142dd9fdc (v2.6.36-rc2-2-g59daa70)
Author: Ma Ling <ling...@intel.com>
Date: Tue Jun 29 03:24:25 2010 +0800
x86, mem: Optimize memcpy by avoiding memory false dependece
Which means btrfs passes overlapping areas to memcpy. I've added some debug info
and found out rough place:
touching files 1 .. 11
#run> touch 1 2 3 4 5 6 7 8 9 10 11
[ 2.270000] memcpy overlap detected: memcpy(dst=0000000070654e8a,
src=0000000070654ea9, size=171) [delta=31]
[ 2.270000] ------------[ cut here ]------------
[ 2.270000] WARNING: at /home/slyfox/linux-2.6/fs/btrfs/memcpy_debug.c:18
btrfs_memcpy+0x52/0x68()
[ 2.270000] Call Trace:
[ 2.270000] 7064b748: [<600eff46>] map_extent_buffer+0x62/0x9e
[ 2.270000] 7064b758: [<60029ad9>] warn_slowpath_common+0x59/0x70
[ 2.270000] 7064b798: [<60029b05>] warn_slowpath_null+0x15/0x17
[ 2.270000] 7064b7a8: [<6011129e>] btrfs_memcpy+0x52/0x68
[ 2.270000] 7064b7d8: [<600efa01>] memcpy_extent_buffer+0x18d/0x1da
[ 2.270000] 7064b858: [<600efae2>] memmove_extent_buffer+0x94/0x208
[ 2.270000] 7064b8d8: [<600bc4b0>] setup_items_for_insert+0x2b8/0x426
[ 2.270000] 7064b8e8: [<600bb25a>] btrfs_leaf_free_space+0x62/0xa6
[ 2.270000] 7064b9c8: [<600c13f3>] btrfs_insert_empty_items+0xa3/0xb5
[ 2.270000] 7064ba38: [<600ce690>] insert_with_overflow+0x33/0xf1
[ 2.270000] 7064ba88: [<600ce7d4>] btrfs_insert_dir_item+0x86/0x268
[ 2.270000] 7064bae8: [<601b498b>] _raw_spin_unlock+0x9/0xb
[ 2.270000] 7064bb48: [<600ddef1>] btrfs_add_link+0x10d/0x170
[ 2.270000] 7064bbc8: [<600ddf7a>] btrfs_add_nondir+0x26/0x52
[ 2.270000] 7064bc08: [<600de73f>] btrfs_create+0xf2/0x1c0
[ 2.270000] 7064bc18: [<6007ccff>] generic_permission+0x57/0x9d
[ 2.270000] 7064bc68: [<6007cf60>] vfs_create+0x6a/0x75
which is in extent_io:copy_pages. I haven't dig further only made sure the
following
patch below (practically converts copy_pages to move_pages). It certainly does
not
look the right thing, but I don't understand extent_io contents yet to
understand what
actually happened.
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 20ddb28..4cab7db 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3893,14 +3893,17 @@ static void copy_pages(struct page *dst_page, struct
page *src_page,
char *src_kaddr;
if (dst_page != src_page)
+ {
src_kaddr = kmap_atomic(src_page, KM_USER1);
+ memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
+ kunmap_atomic(src_kaddr, KM_USER1);
+ }
else
+ {
src_kaddr = dst_kaddr;
-
- memcpy(dst_kaddr + dst_off, src_kaddr + src_off, len);
+ memmove(dst_kaddr + dst_off, src_kaddr + src_off, len);
+ }
kunmap_atomic(dst_kaddr, KM_USER0);
- if (dst_page != src_page)
- kunmap_atomic(src_kaddr, KM_USER1);
}
void memcpy_extent_buffer(struct extent_buffer *dst, unsigned long dst_offset,
--
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