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
