Hi Chris and other btrfs folks, btrfs_mkdir() calls d_instantiate() before unlock_new_inode(), which is wrong because it exposes the inode to lookups before it's been fully initialized. Most filesystems get it right, but f2fs and btrfs don't. I sent a f2fs patch (https://marc.info/?l=linux-fsdevel&m=152409178431350) and was going to send a btrfs patch too, but in btrfs_mkdir() there is actually a comment claiming that the existing order is intentional: d_instantiate(dentry, inode); /* * mkdir is special. We're unlocking after we call d_instantiate * to avoid a race with nfsd calling d_instantiate. */ unlock_new_inode(inode); Unfortunately, I cannot find what it is refering to. The comment was added by commit b0d5d10f41a0 ("Btrfs: use insert_inode_locked4 for inode creation"). Chris, do you remember exactly what you had in mind when you wrote this? And in case anyone wants it, here's a reproducer for the deadlock caused by the current code that calls d_instantiate() before unlock_new_inode(). Note: it needs CONFIG_DEBUG_LOCK_ALLOC=y. #include <sys/stat.h> #include <unistd.h> int main() { struct stat stbuf; if (fork() == 0) { for (;;) stat("dir/file", &stbuf); } else { for (;;) { mkdir("dir", 0777); stat("dir/file", &stbuf); rmdir("dir"); } } } -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
