Hi all:
I am running a redhat 2.6.32-279 offical kernel. Under heavy work
load and memory pressure, in my case, running ltp test for about 20
hours, kernel oops happened. Say concretely, a testcase process open a
file, truncate to 128M, mmap, munmap and close the file, this circle
repeatedly when kernel hangs. Through the vmcore, I also find it hangs
at: BUG_ON(inode->i_data.nrpages) in function clear_inode, which means
the truncate_inode_pages faild to decrase nrpages to 0. I have google
this problem and find no clear solutions but make me confused. The
comment of function truncate_inode_pages says that after it return, the
nrpages may not be zero.
My understanding is: the page reclaime migth still in the process
of deletion of the page. Jan Kara once post a patch, which use spin_lock
to sync the radix tree and nrpages. This kernel already contains this
patch. Then problem come: When kernel hangs, the nrpages is not a small
number like 1 or 2, but a bigger one, more than 500 or 700! So I think
even we take some sync measures before clear inode, the function
truncate_inode_pages together with other reclaim functions failed to set
nrpages to zero. By dump the vmcore, I also find the radix tree is also
not empty but with some slots left.
Then I think:
1. The fault might happen at pagevec_lookup, which return no page
even the radix tree is in fact not empty. Because lookup uses the rcu
lock, is it possible a race condition
happened in the lookup process and lead the function return
unexpectedly? If possiable, how dose it happened ?
2. I find Johannes Weiner post a
patch(http://www.spinics.net/lists/linux-fsdevel/msg72395.html), which
has following code:
+ if (nrpages || nrshadows) {
+ /*
+ * As truncation uses a lockless tree lookup, cycle
+ * the tree lock to make sure any ongoing tree
+ * modification that does not see AS_EXITING is
+ * completed before starting the final truncate.
+ */
+ spin_lock_irq(&mapping->tree_lock);
+ spin_unlock_irq(&mapping->tree_lock);
+
+ truncate_inode_pages(mapping, 0);
+ }
which wrapped the truncate_inode_pages in function
truncate_inode_pages_final. Does it make sence to my problem ?
Any suggestion will be appreciated!
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