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Subject: Re: [PATCH v2] f2fs: fix to avoid NULL pointer dereference on
 se->discard_map
To:     Vicente Bergas <vicencb@gmail.com>
Cc:     jaegeuk@kernel.org, yuchao0@huawei.com,
        linux-f2fs-devel@lists.sourceforge.net,
        linux-kernel@vger.kernel.org
References: <20180903195217.5968-1-chao@kernel.org>
 <CAAMcf8A7WFtNmcpVFSZeMy=n08x7_icAspc=iS9cYo8WnZi-Ng@mail.gmail.com>
From:   Chao Yu <chao@kernel.org>
Message-ID: <2fad4199-8193-a7ad-fc33-9591fa915839@kernel.org>
Date:   Tue, 4 Sep 2018 23:45:57 +0800
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On 2018/9/4 23:25, Vicente Bergas wrote:
> On Mon, Sep 3, 2018 at 9:52 PM, Chao Yu <chao@kernel.org> wrote:
>> From: Chao Yu <yuchao0@huawei.com>
>>
>> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.kernel.org%2Fshow_bug.cgi%3Fid%3D200951&amp;data=02%7C01%7C%7Cc2be7ee866b04268e69f08d6127aa973%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636716715374991374&amp;sdata=E%2Boli5wWbe97f3QCdmAiIIZPEMInd9u221ldtVDqvtA%3D&amp;reserved=0
>>
>> 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://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbbs.archlinux.org%2Fviewtopic.php%3Fid%3D236280&amp;data=02%7C01%7C%7Cc2be7ee866b04268e69f08d6127aa973%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C636716715374991374&amp;sdata=tLP2J%2BL2MPDnqbLm1JcmJ7HfM%2F9j%2F0xc2MET2QSAjVE%3D&amp;reserved=0
>>
>>  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@huawei.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?

You can check discard trace:

echo 1 > /sys/kernel/debug/tracing/events/f2fs/f2fs_issue_discard/enable
cat /sys/kernel/debug/tracing/trace_pipe

Thanks,

> 
> Tested-by: Vicente Bergas <vicencb@gmail.com>
> 
> Regards,
>   Vicenç.
>