Date:   Tue, 4 Sep 2018 17:25:32 +0200
From:   Vicente Bergas <vicencb@...il.com>
To:     Chao Yu <chao@...nel.org>
Cc:     jaegeuk@...nel.org, yuchao0@...wei.com,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: fix to avoid NULL pointer dereference on se->discard_map

On Mon, Sep 3, 2018 at 9:52 PM, Chao Yu <chao@...nel.org> wrote:
> From: Chao Yu <yuchao0@...wei.com>
>
> https://bugzilla.kernel.org/show_bug.cgi?id=200951
>
> These is a NULL pointer dereference issue reported in bugzilla:
>
> Hi,
> in the setup there is a SATA SSD connected to a SATA-to-USB bridge.
>
> The disc is "Samsung SSD 850 PRO 256G" which supports TRIM.
> There are four partitions:
>  sda1: FAT  /boot
>  sda2: F2FS /
>  sda3: F2FS /home
>  sda4: F2FS
>
> The bridge is ASMT1153e which uses the "uas" driver.
> There is no TRIM pass-through, so, when mounting it reports:
>  mounting with "discard" option, but the device does not support discard
>
> The USB host is USB3.0 and UASP capable. It is the one on RK3399.
>
> Given this everything works fine, except there is no TRIM support.
>
> In order to enable TRIM a new UDEV rule is added [1]:
>  /etc/udev/rules.d/10-sata-bridge-trim.rules:
>  ACTION=="add|change", ATTRS{idVendor}=="174c", ATTRS{idProduct}=="55aa", SUBSYSTEM=="scsi_disk", ATTR{provisioning_mode}="unmap"
> After reboot any F2FS write hangs forever and dmesg reports:
>  Unable to handle kernel NULL pointer dereference
>
> Also tested on a x86_64 system: works fine even with TRIM enabled.
>  same disc
>  same bridge
>  different usb host controller
>  different cpu architecture
>  not root filesystem
>
> Regards,
>   Vicenç.
>
> [1] Post #5 in https://bbs.archlinux.org/viewtopic.php?id=236280
>
>  Unable to handle kernel NULL pointer dereference at virtual address 000000000000003e
>  Mem abort info:
>    ESR = 0x96000004
>    Exception class = DABT (current EL), IL = 32 bits
>    SET = 0, FnV = 0
>    EA = 0, S1PTW = 0
>  Data abort info:
>    ISV = 0, ISS = 0x00000004
>    CM = 0, WnR = 0
>  user pgtable: 4k pages, 48-bit VAs, pgdp = 00000000626e3122
>  [000000000000003e] pgd=0000000000000000
>  Internal error: Oops: 96000004 [#1] SMP
>  Modules linked in: overlay snd_soc_hdmi_codec rc_cec dw_hdmi_i2s_audio dw_hdmi_cec snd_soc_simple_card snd_soc_simple_card_utils snd_soc_rockchip_i2s rockchip_rga snd_soc_rockchip_pcm rockchipdrm videobuf2_dma_sg v4l2_mem2mem rtc_rk808 videobuf2_memops analogix_dp videobuf2_v4l2 videobuf2_common dw_hdmi dw_wdt cec rc_core videodev drm_kms_helper media drm rockchip_thermal rockchip_saradc realtek drm_panel_orientation_quirks syscopyarea sysfillrect sysimgblt fb_sys_fops dwmac_rk stmmac_platform stmmac pwm_bl squashfs loop crypto_user gpio_keys hid_kensington
>  CPU: 5 PID: 957 Comm: nvim Not tainted 4.19.0-rc1-1-ARCH #1
>  Hardware name: Sapphire-RK3399 Board (DT)
>  pstate: 00000005 (nzcv daif -PAN -UAO)
>  pc : update_sit_entry+0x304/0x4b0
>  lr : update_sit_entry+0x108/0x4b0
>  sp : ffff00000ca13bd0
>  x29: ffff00000ca13bd0 x28: 000000000000003e
>  x27: 0000000000000020 x26: 0000000000080000
>  x25: 0000000000000048 x24: ffff8000ebb85cf8
>  x23: 0000000000000253 x22: 00000000ffffffff
>  x21: 00000000000535f2 x20: 00000000ffffffdf
>  x19: ffff8000eb9e6800 x18: ffff8000eb9e6be8
>  x17: 0000000007ce6926 x16: 000000001c83ffa8
>  x15: 0000000000000000 x14: ffff8000f602df90
>  x13: 0000000000000006 x12: 0000000000000040
>  x11: 0000000000000228 x10: 0000000000000000
>  x9 : 0000000000000000 x8 : 0000000000000000
>  x7 : 00000000000535f2 x6 : ffff8000ebff3440
>  x5 : ffff8000ebff3440 x4 : ffff8000ebe3a6c8
>  x3 : 00000000ffffffff x2 : 0000000000000020
>  x1 : 0000000000000000 x0 : ffff8000eb9e5800
>  Process nvim (pid: 957, stack limit = 0x0000000063a78320)
>  Call trace:
>   update_sit_entry+0x304/0x4b0
>   f2fs_invalidate_blocks+0x98/0x140
>   truncate_node+0x90/0x400
>   f2fs_remove_inode_page+0xe8/0x340
>   f2fs_evict_inode+0x2b0/0x408
>   evict+0xe0/0x1e0
>   iput+0x160/0x260
>   do_unlinkat+0x214/0x298
>   __arm64_sys_unlinkat+0x3c/0x68
>   el0_svc_handler+0x94/0x118
>   el0_svc+0x8/0xc
>  Code: f9400800 b9488400 36080140 f9400f01 (387c4820)
>  ---[ end trace a0f21a307118c477 ]---
>
> The reason is it is possible to enable discard flag on block queue via
> UDEV, but during mount, f2fs will initialize se->discard_map only if
> this flag is set, once the flag is set after mount, f2fs may dereference
> NULL pointer on se->discard_map.
>
> So this patch does below changes to fix this issue:
> - initialize and update se->discard_map all the time.
> - don't clear DISCARD option if device has no QUEUE_FLAG_DISCARD flag
> during mount.
> - don't issue small discard on zoned block device.
> - introduce some functions to enhance the readability.
>
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
> v2:
> - rebase to last dev branch.
>  fs/f2fs/debug.c   |  3 +--
>  fs/f2fs/f2fs.h    | 15 ++++++++---
>  fs/f2fs/file.c    |  2 +-
>  fs/f2fs/segment.c | 65 ++++++++++++++++++++---------------------------
>  fs/f2fs/super.c   | 16 +++---------
>  5 files changed, 46 insertions(+), 55 deletions(-)
>
> diff --git a/fs/f2fs/debug.c b/fs/f2fs/debug.c
> index 214a968962a1..ebe649d9793c 100644
> --- a/fs/f2fs/debug.c
> +++ b/fs/f2fs/debug.c
> @@ -190,8 +190,7 @@ static void update_mem_info(struct f2fs_sb_info *sbi)
>         si->base_mem += MAIN_SEGS(sbi) * sizeof(struct seg_entry);
>         si->base_mem += f2fs_bitmap_size(MAIN_SEGS(sbi));
>         si->base_mem += 2 * SIT_VBLOCK_MAP_SIZE * MAIN_SEGS(sbi);
> -       if (f2fs_discard_en(sbi))
> -               si->base_mem += SIT_VBLOCK_MAP_SIZE * MAIN_SEGS(sbi);
> +       si->base_mem += SIT_VBLOCK_MAP_SIZE * MAIN_SEGS(sbi);
>         si->base_mem += SIT_VBLOCK_MAP_SIZE;
>         if (sbi->segs_per_sec > 1)
>                 si->base_mem += MAIN_SECS(sbi) * sizeof(struct sec_entry);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index 96bde026636f..b575ec75ef87 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -3399,11 +3399,20 @@ static inline int get_blkz_type(struct f2fs_sb_info *sbi,
>  }
>  #endif
>
> -static inline bool f2fs_discard_en(struct f2fs_sb_info *sbi)
> +static inline bool f2fs_hw_should_discard(struct f2fs_sb_info *sbi)
>  {
> -       struct request_queue *q = bdev_get_queue(sbi->sb->s_bdev);
> +       return f2fs_sb_has_blkzoned(sbi->sb);
> +}
>
> -       return blk_queue_discard(q) || f2fs_sb_has_blkzoned(sbi->sb);
> +static inline bool f2fs_hw_support_discard(struct f2fs_sb_info *sbi)
> +{
> +       return blk_queue_discard(bdev_get_queue(sbi->sb->s_bdev));
> +}
> +
> +static inline bool f2fs_realtime_discard_enable(struct f2fs_sb_info *sbi)
> +{
> +       return (test_opt(sbi, DISCARD) && f2fs_hw_support_discard(sbi)) ||
> +                                       f2fs_hw_should_discard(sbi);
>  }
>
>  static inline void set_opt_mode(struct f2fs_sb_info *sbi, unsigned int mt)
> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> index 5474aaa274b9..ca66b3eb197a 100644
> --- a/fs/f2fs/file.c
> +++ b/fs/f2fs/file.c
> @@ -1978,7 +1978,7 @@ static int f2fs_ioc_fitrim(struct file *filp, unsigned long arg)
>         if (!capable(CAP_SYS_ADMIN))
>                 return -EPERM;
>
> -       if (!blk_queue_discard(q))
> +       if (!f2fs_hw_support_discard(F2FS_SB(sb)))
>                 return -EOPNOTSUPP;
>
>         if (copy_from_user(&range, (struct fstrim_range __user *)arg,
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 30779aaa9dba..c372ff755818 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -1725,11 +1725,11 @@ static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc,
>         struct list_head *head = &SM_I(sbi)->dcc_info->entry_list;
>         int i;
>
> -       if (se->valid_blocks == max_blocks || !f2fs_discard_en(sbi))
> +       if (se->valid_blocks == max_blocks || !f2fs_hw_support_discard(sbi))
>                 return false;
>
>         if (!force) {
> -               if (!test_opt(sbi, DISCARD) || !se->valid_blocks ||
> +               if (!f2fs_realtime_discard_enable(sbi) || !se->valid_blocks ||
>                         SM_I(sbi)->dcc_info->nr_discards >=
>                                 SM_I(sbi)->dcc_info->max_discards)
>                         return false;
> @@ -1835,7 +1835,7 @@ void f2fs_clear_prefree_segments(struct f2fs_sb_info *sbi,
>                                 dirty_i->nr_dirty[PRE]--;
>                 }
>
> -               if (!test_opt(sbi, DISCARD))
> +               if (!f2fs_realtime_discard_enable(sbi))
>                         continue;
>
>                 if (force && start >= cpc->trim_start &&
> @@ -2025,8 +2025,7 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
>                         del = 0;
>                 }
>
> -               if (f2fs_discard_en(sbi) &&
> -                       !f2fs_test_and_set_bit(offset, se->discard_map))
> +               if (!f2fs_test_and_set_bit(offset, se->discard_map))
>                         sbi->discard_blks--;
>
>                 /* don't overwrite by SSR to keep node chain */
> @@ -2054,8 +2053,7 @@ static void update_sit_entry(struct f2fs_sb_info *sbi, block_t blkaddr, int del)
>                         del = 0;
>                 }
>
> -               if (f2fs_discard_en(sbi) &&
> -                       f2fs_test_and_clear_bit(offset, se->discard_map))
> +               if (f2fs_test_and_clear_bit(offset, se->discard_map))
>                         sbi->discard_blks++;
>         }
>         if (!f2fs_test_bit(offset, se->ckpt_valid_map))
> @@ -2671,7 +2669,7 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
>          * discard option. User configuration looks like using runtime discard
>          * or periodic fstrim instead of it.
>          */
> -       if (test_opt(sbi, DISCARD))
> +       if (f2fs_realtime_discard_enable(sbi))
>                 goto out;
>
>         start_block = START_BLOCK(sbi, start_segno);
> @@ -3762,13 +3760,11 @@ static int build_sit_info(struct f2fs_sb_info *sbi)
>                         return -ENOMEM;
>  #endif
>
> -               if (f2fs_discard_en(sbi)) {
> -                       sit_i->sentries[start].discard_map
> -                               = f2fs_kzalloc(sbi, SIT_VBLOCK_MAP_SIZE,
> -                                                               GFP_KERNEL);
> -                       if (!sit_i->sentries[start].discard_map)
> -                               return -ENOMEM;
> -               }
> +               sit_i->sentries[start].discard_map
> +                       = f2fs_kzalloc(sbi, SIT_VBLOCK_MAP_SIZE,
> +                                                       GFP_KERNEL);
> +               if (!sit_i->sentries[start].discard_map)
> +                       return -ENOMEM;
>         }
>
>         sit_i->tmp_map = f2fs_kzalloc(sbi, SIT_VBLOCK_MAP_SIZE, GFP_KERNEL);
> @@ -3916,18 +3912,16 @@ static int build_sit_entries(struct f2fs_sb_info *sbi)
>                                 total_node_blocks += se->valid_blocks;
>
>                         /* build discard map only one time */
> -                       if (f2fs_discard_en(sbi)) {
> -                               if (is_set_ckpt_flags(sbi, CP_TRIMMED_FLAG)) {
> -                                       memset(se->discard_map, 0xff,
> -                                               SIT_VBLOCK_MAP_SIZE);
> -                               } else {
> -                                       memcpy(se->discard_map,
> -                                               se->cur_valid_map,
> -                                               SIT_VBLOCK_MAP_SIZE);
> -                                       sbi->discard_blks +=
> -                                               sbi->blocks_per_seg -
> -                                               se->valid_blocks;
> -                               }
> +                       if (is_set_ckpt_flags(sbi, CP_TRIMMED_FLAG)) {
> +                               memset(se->discard_map, 0xff,
> +                                       SIT_VBLOCK_MAP_SIZE);
> +                       } else {
> +                               memcpy(se->discard_map,
> +                                       se->cur_valid_map,
> +                                       SIT_VBLOCK_MAP_SIZE);
> +                               sbi->discard_blks +=
> +                                       sbi->blocks_per_seg -
> +                                       se->valid_blocks;
>                         }
>
>                         if (sbi->segs_per_sec > 1)
> @@ -3965,16 +3959,13 @@ static int build_sit_entries(struct f2fs_sb_info *sbi)
>                 if (IS_NODESEG(se->type))
>                         total_node_blocks += se->valid_blocks;
>
> -               if (f2fs_discard_en(sbi)) {
> -                       if (is_set_ckpt_flags(sbi, CP_TRIMMED_FLAG)) {
> -                               memset(se->discard_map, 0xff,
> -                                                       SIT_VBLOCK_MAP_SIZE);
> -                       } else {
> -                               memcpy(se->discard_map, se->cur_valid_map,
> -                                                       SIT_VBLOCK_MAP_SIZE);
> -                               sbi->discard_blks += old_valid_blocks;
> -                               sbi->discard_blks -= se->valid_blocks;
> -                       }
> +               if (is_set_ckpt_flags(sbi, CP_TRIMMED_FLAG)) {
> +                       memset(se->discard_map, 0xff, SIT_VBLOCK_MAP_SIZE);
> +               } else {
> +                       memcpy(se->discard_map, se->cur_valid_map,
> +                                               SIT_VBLOCK_MAP_SIZE);
> +                       sbi->discard_blks += old_valid_blocks;
> +                       sbi->discard_blks -= se->valid_blocks;
>                 }
>
>                 if (sbi->segs_per_sec > 1) {
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 53d70b64fea1..5cad0f7687e9 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -360,7 +360,6 @@ static int f2fs_check_quota_options(struct f2fs_sb_info *sbi)
>  static int parse_options(struct super_block *sb, char *options)
>  {
>         struct f2fs_sb_info *sbi = F2FS_SB(sb);
> -       struct request_queue *q;
>         substring_t args[MAX_OPT_ARGS];
>         char *p, *name;
>         int arg = 0;
> @@ -415,14 +414,7 @@ static int parse_options(struct super_block *sb, char *options)
>                                 return -EINVAL;
>                         break;
>                 case Opt_discard:
> -                       q = bdev_get_queue(sb->s_bdev);
> -                       if (blk_queue_discard(q)) {
> -                               set_opt(sbi, DISCARD);
> -                       } else if (!f2fs_sb_has_blkzoned(sb)) {
> -                               f2fs_msg(sb, KERN_WARNING,
> -                                       "mounting with \"discard\" option, but "
> -                                       "the device does not support discard");
> -                       }
> +                       set_opt(sbi, DISCARD);
>                         break;
>                 case Opt_nodiscard:
>                         if (f2fs_sb_has_blkzoned(sb)) {
> @@ -1032,7 +1024,8 @@ static void f2fs_put_super(struct super_block *sb)
>         /* be sure to wait for any on-going discard commands */
>         dropped = f2fs_wait_discard_bios(sbi);
>
> -       if (f2fs_discard_en(sbi) && !sbi->discard_blks && !dropped) {
> +       if ((f2fs_hw_support_discard(sbi) || f2fs_hw_should_discard(sbi)) &&
> +                                       !sbi->discard_blks && !dropped) {
>                 struct cp_control cpc = {
>                         .reason = CP_UMOUNT | CP_TRIMMED,
>                 };
> @@ -1399,8 +1392,7 @@ static void default_options(struct f2fs_sb_info *sbi)
>         set_opt(sbi, NOHEAP);
>         sbi->sb->s_flags |= SB_LAZYTIME;
>         set_opt(sbi, FLUSH_MERGE);
> -       if (blk_queue_discard(bdev_get_queue(sbi->sb->s_bdev)))
> -               set_opt(sbi, DISCARD);
> +       set_opt(sbi, DISCARD);
>         if (f2fs_sb_has_blkzoned(sbi->sb))
>                 set_opt_mode(sbi, F2FS_MOUNT_LFS);
>         else
> --
> 2.18.0
>

Hi,
just tested and it works fine: no more segfaults.
How can i check that TRIM is indeed being used?

Tested-by: Vicente Bergas <vicencb@...il.com>

Regards,
  Vicenç.

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