ext4: allow readdir()'s of large empty directories to be interrupted

If a directory has a large number of empty blocks, iterating over all
of them can take a long time, leading to scheduler warnings and users
getting irritated when they can't kill a process in the middle of one
of these long-running readdir operations.  Fix this by adding checks to
ext4_readdir() and ext4_htree_fill_tree().

This was reverted earlier due to a typo in the original commit where I
experimented with using signal_pending() instead of
fatal_signal_pending().  The test was in the wrong place if we were
going to return signal_pending() since we would end up returning
duplicant entries.  See 9f2394c9be47 for a more detailed explanation.

Added fix as suggested by Linus to check for signal_pending() in
in the filldir() functions.

Reported-by: Benjamin LaHaise <bcrl@kvack.org>
Google-Bug-Id: 27880676
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/compat.c b/fs/compat.c
index a71936a3f4cb39e7022d98363a0df70d69c8c3d0..f940cb20562fc2c593e4f962f747149f6b067c10 100644 (file)
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -936,6 +936,8 @@ static int compat_filldir(struct dir_context *ctx, const char *name, int namlen,
        }
        dirent = buf->previous;
        if (dirent) {
+               if (signal_pending(current))
+                       return -EINTR;
                if (__put_user(offset, &dirent->d_off))
                        goto efault;
        }
@@ -1020,6 +1022,8 @@ static int compat_filldir64(struct dir_context *ctx, const char *name,
        dirent = buf->previous;
 
        if (dirent) {
+               if (signal_pending(current))
+                       return -EINTR;
                if (__put_user_unaligned(offset, &dirent->d_off))
                        goto efault;
        }

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index 561d7308b393a0347dea3b1344f409bf5fed0139..4173bfe21114fb94f644e5d5917711aba7deab88 100644 (file)
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -150,6 +150,11 @@ static int ext4_readdir(struct file *file, struct dir_context *ctx)
        while (ctx->pos < inode->i_size) {
                struct ext4_map_blocks map;
 
+               if (fatal_signal_pending(current)) {
+                       err = -ERESTARTSYS;
+                       goto errout;
+               }
+               cond_resched();
                map.m_lblk = ctx->pos >> EXT4_BLOCK_SIZE_BITS(sb);
                map.m_len = 1;
                err = ext4_map_blocks(NULL, inode, &map, 0);

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 48e4b8907826eca52a1e94e14bdfdb0fd2240c56..c07422d254b64a3126f6368419a5ac5fa0c0323b 100644 (file)
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -1107,6 +1107,11 @@ int ext4_htree_fill_tree(struct file *dir_file, __u32 start_hash,
        }
 
        while (1) {
+               if (fatal_signal_pending(current)) {
+                       err = -ERESTARTSYS;
+                       goto errout;
+               }
+               cond_resched();
                block = dx_get_block(frame->at);
                ret = htree_dirblock_to_tree(dir_file, dir, block, &hinfo,
                                             start_hash, start_minor_hash);

diff --git a/fs/readdir.c b/fs/readdir.c
index e69ef3b79787b9fb4f02ab65b35c28571c9df1a0..5f2d4bee5a73dc92151f08af658a3d29e64bda87 100644 (file)
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -169,6 +169,8 @@ static int filldir(struct dir_context *ctx, const char *name, int namlen,
        }
        dirent = buf->previous;
        if (dirent) {
+               if (signal_pending(current))
+                       return -EINTR;
                if (__put_user(offset, &dirent->d_off))
                        goto efault;
        }
@@ -248,6 +250,8 @@ static int filldir64(struct dir_context *ctx, const char *name, int namlen,
                return -EINVAL;
        dirent = buf->previous;
        if (dirent) {
+               if (signal_pending(current))
+                       return -EINTR;
                if (__put_user(offset, &dirent->d_off))
                        goto efault;
        }