The patch titled
Subject: tmpfs: change final i_blocks BUG to WARNING
has been added to the -mm tree. Its filename is
tmpfs-change-final-i_blocks-bug-to-warning.patch
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From: Hugh Dickins <hughd@xxxxxxxxxx>
Subject: tmpfs: change final i_blocks BUG to WARNING
Under a particular load on one machine, I have hit shmem_evict_inode()'s
BUG_ON(inode->i_blocks), enough times to narrow it down to a particular
race between swapout and eviction.
It comes from the "if (freed > 0)" asymmetry in shmem_recalc_inode(), and
the lack of coherent locking between mapping's nrpages and shmem's swapped
count. There's a window in shmem_writepage(), between lowering nrpages in
shmem_delete_from_page_cache() and then raising swapped count, when the
freed count appears to be +1 when it should be 0, and then the asymmetry
stops it from being corrected with -1 before hitting the BUG.
One answer is coherent locking: using tree_lock throughout, without
info->lock; reasonable, but the raw_spin_lock in percpu_counter_add() on
used_blocks makes that messier than expected. Another answer may be a
further effort to eliminate the weird shmem_recalc_inode() altogether, but
previous attempts at that failed.
So far undecided, but for now change the BUG_ON to WARN_ON: in usual
circumstances it remains a useful consistency check.
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff -puN mm/shmem.c~tmpfs-change-final-i_blocks-bug-to-warning mm/shmem.c
--- a/mm/shmem.c~tmpfs-change-final-i_blocks-bug-to-warning
+++ a/mm/shmem.c
@@ -643,7 +643,7 @@ static void shmem_evict_inode(struct ino
kfree(info->symlink);
simple_xattrs_free(&info->xattrs);
- BUG_ON(inode->i_blocks);
+ WARN_ON(inode->i_blocks);
shmem_free_inode(inode->i_sb);
clear_inode(inode);
}
_
Patches currently in -mm which might be from hughd@xxxxxxxxxx are
linux-next.patch
tmpfs-fix-shmem_getpage_gfp-vm_bug_on.patch
tmpfs-change-final-i_blocks-bug-to-warning.patch
mm-add-comment-on-storage-key-dirty-bit-semantics.patch
mm-refactor-reinsert-of-swap_info-in-sys_swapoff.patch
mm-do-not-call-frontswap_init-during-swapoff.patch
swap-add-a-simple-detector-for-inappropriate-swapin-readahead.patch
swap-add-a-simple-detector-for-inappropriate-swapin-readahead-fix.patch
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