[XFS] revert to double-buffering readdir

The current readdir implementation deadlocks on a btree buffers locks
because nfsd calls back into ->lookup from the filldir callback. The only
short-term fix for this is to revert to the old inefficient
double-buffering scheme.

SGI-PV: 973377
SGI-Modid: xfs-linux-melb:xfs-kern:30201a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>

1 files changed, 124 insertions, 0 deletions

diff --git a/fs/xfs/linux-2.6/xfs_file.c b/fs/xfs/linux-2.6/xfs_file.c
index fb8dd34041eb..54c564693d93 100644
--- a/fs/xfs/linux-2.6/xfs_file.c
+++ b/fs/xfs/linux-2.6/xfs_file.c
@@ -218,6 +218,15 @@ xfs_vm_fault(
 }
 #endif /* CONFIG_XFS_DMAPI */
 
+/*
+ * Unfortunately we can't just use the clean and simple readdir implementation
+ * below, because nfs might call back into ->lookup from the filldir callback
+ * and that will deadlock the low-level btree code.
+ *
+ * Hopefully we'll find a better workaround that allows to use the optimal
+ * version at least for local readdirs for 2.6.25.
+ */
+#if 0
 STATIC int
 xfs_file_readdir(
         struct file     *filp,
@@ -249,6 +258,121 @@ xfs_file_readdir(
                 return -error;
         return 0;
 }
+#else
+
+struct hack_dirent {
+        int             namlen;
+        loff_t          offset;
+        u64             ino;
+        unsigned int    d_type;
+        char            name[];
+};
+
+struct hack_callback {
+        char            *dirent;
+        size_t          len;
+        size_t          used;
+};
+
+STATIC int
+xfs_hack_filldir(
+        void            *__buf,
+        const char      *name,
+        int             namlen,
+        loff_t          offset,
+        u64             ino,
+        unsigned int    d_type)
+{
+        struct hack_callback *buf = __buf;
+        struct hack_dirent *de = (struct hack_dirent *)(buf->dirent + buf->used);
+
+        if (buf->used + sizeof(struct hack_dirent) + namlen > buf->len)
+                return -EINVAL;
+
+        de->namlen = namlen;
+        de->offset = offset;
+        de->ino = ino;
+        de->d_type = d_type;
+        memcpy(de->name, name, namlen);
+        buf->used += sizeof(struct hack_dirent) + namlen;
+        return 0;
+}
+
+STATIC int
+xfs_file_readdir(
+        struct file     *filp,
+        void            *dirent,
+        filldir_t       filldir)
+{
+        struct inode    *inode = filp->f_path.dentry->d_inode;
+        xfs_inode_t     *ip = XFS_I(inode);
+        struct hack_callback buf;
+        struct hack_dirent *de;
+        int             error;
+        loff_t          size;
+        int             eof = 0;
+        xfs_off_t       start_offset, curr_offset, offset;
+
+        /*
+         * Try fairly hard to get memory
+         */
+        buf.len = PAGE_CACHE_SIZE;
+        do {
+                buf.dirent = kmalloc(buf.len, GFP_KERNEL);
+                if (buf.dirent)
+                        break;
+                buf.len >>= 1;
+        } while (buf.len >= 1024);
+
+        if (!buf.dirent)
+                return -ENOMEM;
+
+        curr_offset = filp->f_pos;
+        if (curr_offset == 0x7fffffff)
+                offset = 0xffffffff;
+        else
+                offset = filp->f_pos;
+
+        while (!eof) {
+                int reclen;
+                start_offset = offset;
+
+                buf.used = 0;
+                error = -xfs_readdir(ip, &buf, buf.len, &offset,
+                                     xfs_hack_filldir);
+                if (error || offset == start_offset) {
+                        size = 0;
+                        break;
+                }
+
+                size = buf.used;
+                de = (struct hack_dirent *)buf.dirent;
+                while (size > 0) {
+                        if (filldir(dirent, de->name, de->namlen,
+                                        curr_offset & 0x7fffffff,
+                                        de->ino, de->d_type)) {
+                                goto done;
+                        }
+
+                        reclen = sizeof(struct hack_dirent) + de->namlen;
+                        size -= reclen;
+                        curr_offset = de->offset /* & 0x7fffffff */;
+                        de = (struct hack_dirent *)((char *)de + reclen);
+                }
+        }
+
+ done:
+        if (!error) {
+                if (size == 0)
+                        filp->f_pos = offset & 0x7fffffff;
+                else if (de)
+                        filp->f_pos = curr_offset;
+        }
+
+        kfree(buf.dirent);
+        return error;
+}
+#endif
 
 STATIC int
 xfs_file_mmap(