On 9/30/21 8:41 AM, Song Liu wrote:
On Wed, Sep 29, 2021 at 5:02 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
On Wed, Sep 29, 2021 at 04:41:48PM -0700, Song Liu wrote:
The issue is NOT caused by concurrent khugepaged:collapse_file() and
truncate_pagecache(inode, 0). With some printks, we can see a clear
time gap (>2 second ) between collapse_file() finishes, and
truncate_pagecache() (which crashes soon). Therefore, my earlier
suggestion that adds deny_write_access() to collapse_file() does NOT
work.
The crash is actually caused by concurrent truncate_pagecache(inode, 0).
If I change the number of write thread in stress_madvise_dso.c to one,
(IOW, one thread_read and one thread_write), I cannot reproduce the
crash anymore.
I think this means we cannot fix this issue in collapse_file(), because it
finishes long before the crash.
Ah! So are we missing one or more of these locks:
inode_lock(inode);
filemap_invalidate_lock(mapping);
in the open path?
The following fixes the crash in my test. But I am not sure whether this is the
best fix.
Rongwei, could you please run more tests on it?
Yes, I'd like to.
Thanks,
Song
diff --git i/fs/open.c w/fs/open.c
index daa324606a41f..d13c4668b2e53 100644
--- i/fs/open.c
+++ w/fs/open.c
@@ -856,8 +856,11 @@ static int do_dentry_open(struct file *f,
* of THPs into the page cache will fail.
*/
smp_mb();
- if (filemap_nr_thps(inode->i_mapping))
+ if (filemap_nr_thps(inode->i_mapping)) {
+ filemap_invalidate_lock(inode->i_mapping);
Learned something, Thanks!
But, the race between collapse_file and truncate_pagecache, I am not
sure whether it exists or not. If exists, whether this patch only can
fix truncate_pagecache concurrent?
Anyway, I will run more tests on it at first.
Thanks!
truncate_pagecache(inode, 0);
+ filemap_invalidate_unlock(inode->i_mapping);
+ }
}
return 0;
