Messages in this thread | | | From | Anton Altaparmakov <> | Subject | Race condition between iget_locked() and evict_inodes() | Date | Thu, 29 Sep 2016 11:53:21 +0000 |
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Hi Al,
I think there is a race condition between iget_locked() and evict_inodes().
evict_inodes() checks i_count and if zero proceeds to take i_lock then set I_FREEING and eventually disposes of the inode.
But a concurrent iget_locked() takes i_lock and then increments i_count.
Thus if the events happen in this order:
evict_inodes() iget_locked() in find_inode_fast() atomic_read(&inode->i_count) -> 0 take i_lock wait on i_lock __iget(inode); -> i_count now 1 set I_FREEING drop i_lock evict() return inode to caller
The inode is now gone due to the evict() call whilst it is happily being used with an elevated i_count by the iget_locked() calling process. It seems to me like evict_inodes() should be checking i_count inside i_lock either as the only check or it should at least re-check it.
Please tell me what I am missing here. I assume there must be something providing exclusion and I am just too blind to see it but I thought it worth bringing to your attention in case it really is simply broken.
Best regards,
Anton -- Anton Altaparmakov <anton at tuxera.com> (replace at with @) Lead in File System Development, Tuxera Inc., http://www.tuxera.com/ Linux NTFS maintainer
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