Re: possible deadlock in shmem_uncharge

From: Yang Shi
Date: Mon Apr 13 2020 - 18:10:40 EST

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On Sun, Apr 12, 2020 at 3:11 AM syzbot
<syzbot+c8a8197c8852f566b9d9@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: ae46d2aa mm/gup: Let __get_user_pages_locked() return -EIN..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=14a30a77e00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=ca75979eeebf06c2
> dashboard link: https://syzkaller.appspot.com/bug?extid=c8a8197c8852f566b9d9
> compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15f5632be00000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=132ade57e00000
>
> The bug was bisected to:
>
> commit 71725ed10c40696dc6bdccf8e225815dcef24dba
> Author: Hugh Dickins <hughd@xxxxxxxxxx>
> Date: Tue Apr 7 03:07:57 2020 +0000
>
> mm: huge tmpfs: try to split_huge_page() when punching hole
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=120a752be00000
> final crash: https://syzkaller.appspot.com/x/report.txt?x=110a752be00000
> console output: https://syzkaller.appspot.com/x/log.txt?x=160a752be00000
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+c8a8197c8852f566b9d9@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: 71725ed10c40 ("mm: huge tmpfs: try to split_huge_page() when punching hole")
>
> =====================================================
> WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
> 5.6.0-syzkaller #0 Not tainted
> -----------------------------------------------------
> syz-executor428/8337 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> ffff8880a851c778 (&info->lock){....}-{2:2}, at: shmem_uncharge+0x24/0x270 mm/shmem.c:341
>
> and this task is already holding:
> ffff8880a851cac8 (&xa->xa_lock#4){..-.}-{2:2}, at: spin_lock include/linux/spinlock.h:353 [inline]
> ffff8880a851cac8 (&xa->xa_lock#4){..-.}-{2:2}, at: split_huge_page_to_list+0xad0/0x33b0 mm/huge_memory.c:2864
> which would create a new lock dependency:
> (&xa->xa_lock#4){..-.}-{2:2} -> (&info->lock){....}-{2:2}
>
> but this new dependency connects a SOFTIRQ-irq-safe lock:
> (&xa->xa_lock#4){..-.}-{2:2}

It looks shmem_uncharge() is just called by __split_huge_page() and
collapse_file(). The collapse_file() has acquired xa_lock with irq
disabled before acquiring info->lock, so it is safe.
__split_huge_page() is called with holding xa_lock with irq enabled,
but lru_lock is acquired with irq disabled before acquiring xa_lock.

So, it is unnecessary to acquire info->lock with irq disabled in
shmem_uncharge(). Can syzbot try the below patch?

diff --git a/mm/shmem.c b/mm/shmem.c
index d722eb8..100117b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -334,15 +334,14 @@ bool shmem_charge(struct inode *inode, long pages)
void shmem_uncharge(struct inode *inode, long pages)
{
struct shmem_inode_info *info = SHMEM_I(inode);
- unsigned long flags;

/* nrpages adjustment done by __delete_from_page_cache() or caller */

- spin_lock_irqsave(&info->lock, flags);
+ spin_lock(&info->lock);
info->alloced -= pages;
inode->i_blocks -= pages * BLOCKS_PER_PAGE;
shmem_recalc_inode(inode);
- spin_unlock_irqrestore(&info->lock, flags);
+ spin_unlock(&info->lock);

shmem_inode_unacct_blocks(inode, pages);
}

>
> ... which became SOFTIRQ-irq-safe at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> test_clear_page_writeback+0x1d7/0x11e0 mm/page-writeback.c:2728
> end_page_writeback+0x239/0x520 mm/filemap.c:1317
> end_buffer_async_write+0x442/0x5c0 fs/buffer.c:384
> end_bio_bh_io_sync+0xe2/0x140 fs/buffer.c:3012
> bio_endio+0x473/0x820 block/bio.c:1422
> req_bio_endio block/blk-core.c:245 [inline]
> blk_update_request+0x3e1/0xdc0 block/blk-core.c:1472
> scsi_end_request+0x80/0x7b0 drivers/scsi/scsi_lib.c:575
> scsi_io_completion+0x1e7/0x1300 drivers/scsi/scsi_lib.c:959
> scsi_softirq_done+0x31e/0x3b0 drivers/scsi/scsi_lib.c:1454
> blk_done_softirq+0x2db/0x440 block/blk-softirq.c:37
> __do_softirq+0x26c/0x9f7 kernel/softirq.c:292
> invoke_softirq kernel/softirq.c:373 [inline]
> irq_exit+0x192/0x1d0 kernel/softirq.c:413
> exiting_irq arch/x86/include/asm/apic.h:546 [inline]
> do_IRQ+0xda/0x270 arch/x86/kernel/irq.c:263
> ret_from_intr+0x0/0x2b
> arch_local_irq_restore arch/x86/include/asm/paravirt.h:759 [inline]
> lock_acquire+0x267/0x8f0 kernel/locking/lockdep.c:4926
> down_write+0x8d/0x150 kernel/locking/rwsem.c:1531
> inode_lock include/linux/fs.h:797 [inline]
> process_measurement+0x68a/0x1750 security/integrity/ima/ima_main.c:228
> ima_file_check+0xb9/0x100 security/integrity/ima/ima_main.c:440
> do_open fs/namei.c:3231 [inline]
> path_openat+0x1997/0x27d0 fs/namei.c:3346
> do_filp_open+0x192/0x260 fs/namei.c:3373
> do_sys_openat2+0x585/0x7d0 fs/open.c:1148
> do_sys_open+0xc3/0x140 fs/open.c:1164
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
> to a SOFTIRQ-irq-unsafe lock:
> (shmlock_user_lock){+.+.}-{2:2}
>
> ... which became SOFTIRQ-irq-unsafe at:
> ...
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:353 [inline]
> user_shm_lock+0xab/0x230 mm/mlock.c:855
> hugetlb_file_setup+0x4e1/0x677 fs/hugetlbfs/inode.c:1416
> newseg+0x460/0xe60 ipc/shm.c:652
> ipcget_new ipc/util.c:344 [inline]
> ipcget+0xf0/0xcb0 ipc/util.c:643
> ksys_shmget ipc/shm.c:742 [inline]
> __do_sys_shmget ipc/shm.c:747 [inline]
> __se_sys_shmget ipc/shm.c:745 [inline]
> __x64_sys_shmget+0x139/0x1a0 ipc/shm.c:745
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
> other info that might help us debug this:
>
> Chain exists of:
> &xa->xa_lock#4 --> &info->lock --> shmlock_user_lock
>
> Possible interrupt unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(shmlock_user_lock);
> local_irq_disable();
> lock(&xa->xa_lock#4);
> lock(&info->lock);
> <Interrupt>
> lock(&xa->xa_lock#4);
>
> *** DEADLOCK ***
>
> 5 locks held by syz-executor428/8337:
> #0: ffff8880a7948450 (sb_writers#7){.+.+}-{0:0}, at: sb_start_write include/linux/fs.h:1655 [inline]
> #0: ffff8880a7948450 (sb_writers#7){.+.+}-{0:0}, at: do_sys_ftruncate+0x29f/0x570 fs/open.c:190
> #1: ffff8880a851c9d0 (&sb->s_type->i_mutex_key#16){+.+.}-{3:3}, at: inode_lock include/linux/fs.h:797 [inline]
> #1: ffff8880a851c9d0 (&sb->s_type->i_mutex_key#16){+.+.}-{3:3}, at: do_truncate+0x125/0x1f0 fs/open.c:62
> #2: ffff8880a851cb90 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: i_mmap_lock_read include/linux/fs.h:541 [inline]
> #2: ffff8880a851cb90 (&mapping->i_mmap_rwsem){++++}-{3:3}, at: split_huge_page_to_list+0x4c3/0x33b0 mm/huge_memory.c:2825
> #3: ffff88812ffffcd8 (&pgdat->lru_lock){....}-{2:2}, at: split_huge_page_to_list+0x8da/0x33b0 mm/huge_memory.c:2855
> #4: ffff8880a851cac8 (&xa->xa_lock#4){..-.}-{2:2}, at: spin_lock include/linux/spinlock.h:353 [inline]
> #4: ffff8880a851cac8 (&xa->xa_lock#4){..-.}-{2:2}, at: split_huge_page_to_list+0xad0/0x33b0 mm/huge_memory.c:2864
>
> the dependencies between SOFTIRQ-irq-safe lock and the holding lock:
> -> (&xa->xa_lock#4){..-.}-{2:2} {
> IN-SOFTIRQ-W at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> test_clear_page_writeback+0x1d7/0x11e0 mm/page-writeback.c:2728
> end_page_writeback+0x239/0x520 mm/filemap.c:1317
> end_buffer_async_write+0x442/0x5c0 fs/buffer.c:384
> end_bio_bh_io_sync+0xe2/0x140 fs/buffer.c:3012
> bio_endio+0x473/0x820 block/bio.c:1422
> req_bio_endio block/blk-core.c:245 [inline]
> blk_update_request+0x3e1/0xdc0 block/blk-core.c:1472
> scsi_end_request+0x80/0x7b0 drivers/scsi/scsi_lib.c:575
> scsi_io_completion+0x1e7/0x1300 drivers/scsi/scsi_lib.c:959
> scsi_softirq_done+0x31e/0x3b0 drivers/scsi/scsi_lib.c:1454
> blk_done_softirq+0x2db/0x440 block/blk-softirq.c:37
> __do_softirq+0x26c/0x9f7 kernel/softirq.c:292
> invoke_softirq kernel/softirq.c:373 [inline]
> irq_exit+0x192/0x1d0 kernel/softirq.c:413
> exiting_irq arch/x86/include/asm/apic.h:546 [inline]
> do_IRQ+0xda/0x270 arch/x86/kernel/irq.c:263
> ret_from_intr+0x0/0x2b
> arch_local_irq_restore arch/x86/include/asm/paravirt.h:759 [inline]
> lock_acquire+0x267/0x8f0 kernel/locking/lockdep.c:4926
> down_write+0x8d/0x150 kernel/locking/rwsem.c:1531
> inode_lock include/linux/fs.h:797 [inline]
> process_measurement+0x68a/0x1750 security/integrity/ima/ima_main.c:228
> ima_file_check+0xb9/0x100 security/integrity/ima/ima_main.c:440
> do_open fs/namei.c:3231 [inline]
> path_openat+0x1997/0x27d0 fs/namei.c:3346
> do_filp_open+0x192/0x260 fs/namei.c:3373
> do_sys_openat2+0x585/0x7d0 fs/open.c:1148
> do_sys_open+0xc3/0x140 fs/open.c:1164
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> INITIAL USE at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
> _raw_spin_lock_irq+0x5b/0x80 kernel/locking/spinlock.c:167
> spin_lock_irq include/linux/spinlock.h:378 [inline]
> __add_to_page_cache_locked+0x607/0xe00 mm/filemap.c:855
> add_to_page_cache_lru+0x1aa/0x700 mm/filemap.c:921
> do_read_cache_page+0x9ab/0x1810 mm/filemap.c:2755
> read_mapping_page include/linux/pagemap.h:397 [inline]
> read_part_sector+0xf6/0x600 block/partitions/core.c:643
> adfspart_check_ICS+0x9d/0xc80 block/partitions/acorn.c:360
> check_partition block/partitions/core.c:140 [inline]
> blk_add_partitions+0x474/0xe50 block/partitions/core.c:571
> bdev_disk_changed+0x1fb/0x380 fs/block_dev.c:1544
> __blkdev_get+0xb15/0x1530 fs/block_dev.c:1647
> blkdev_get+0x41/0x2b0 fs/block_dev.c:1749
> register_disk block/genhd.c:763 [inline]
> __device_add_disk+0xa4f/0x1170 block/genhd.c:853
> add_disk include/linux/genhd.h:294 [inline]
> brd_init+0x297/0x463 drivers/block/brd.c:533
> do_one_initcall+0x10a/0x7d0 init/main.c:1158
> do_initcall_level init/main.c:1231 [inline]
> do_initcalls init/main.c:1247 [inline]
> do_basic_setup init/main.c:1267 [inline]
> kernel_init_freeable+0x501/0x5ae init/main.c:1451
> kernel_init+0xd/0x1bb init/main.c:1358
> ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
> }
> ... key at: [<ffffffff8c67b1e0>] __key.18007+0x0/0x40
> ... acquired at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> shmem_uncharge+0x24/0x270 mm/shmem.c:341
> __split_huge_page mm/huge_memory.c:2613 [inline]
> split_huge_page_to_list+0x274b/0x33b0 mm/huge_memory.c:2886
> split_huge_page include/linux/huge_mm.h:204 [inline]
> shmem_punch_compound+0x13e/0x1e0 mm/shmem.c:814
> shmem_undo_range+0x5f1/0x1b80 mm/shmem.c:870
> shmem_truncate_range+0x27/0xa0 mm/shmem.c:980
> shmem_setattr+0x8b6/0xc80 mm/shmem.c:1039
> notify_change+0xb6d/0x1020 fs/attr.c:336
> do_truncate+0x134/0x1f0 fs/open.c:64
> do_sys_ftruncate+0x4a5/0x570 fs/open.c:195
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
>
> the dependencies between the lock to be acquired
> and SOFTIRQ-irq-unsafe lock:
> -> (shmlock_user_lock){+.+.}-{2:2} {
> HARDIRQ-ON-W at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:353 [inline]
> user_shm_lock+0xab/0x230 mm/mlock.c:855
> hugetlb_file_setup+0x4e1/0x677 fs/hugetlbfs/inode.c:1416
> newseg+0x460/0xe60 ipc/shm.c:652
> ipcget_new ipc/util.c:344 [inline]
> ipcget+0xf0/0xcb0 ipc/util.c:643
> ksys_shmget ipc/shm.c:742 [inline]
> __do_sys_shmget ipc/shm.c:747 [inline]
> __se_sys_shmget ipc/shm.c:745 [inline]
> __x64_sys_shmget+0x139/0x1a0 ipc/shm.c:745
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> SOFTIRQ-ON-W at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:353 [inline]
> user_shm_lock+0xab/0x230 mm/mlock.c:855
> hugetlb_file_setup+0x4e1/0x677 fs/hugetlbfs/inode.c:1416
> newseg+0x460/0xe60 ipc/shm.c:652
> ipcget_new ipc/util.c:344 [inline]
> ipcget+0xf0/0xcb0 ipc/util.c:643
> ksys_shmget ipc/shm.c:742 [inline]
> __do_sys_shmget ipc/shm.c:747 [inline]
> __se_sys_shmget ipc/shm.c:745 [inline]
> __x64_sys_shmget+0x139/0x1a0 ipc/shm.c:745
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> INITIAL USE at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:353 [inline]
> user_shm_lock+0xab/0x230 mm/mlock.c:855
> shmem_lock+0x1dd/0x2d0 mm/shmem.c:2184
> shmctl_do_lock+0x73f/0x8f0 ipc/shm.c:1111
> ksys_shmctl.constprop.0+0x203/0x350 ipc/shm.c:1188
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> }
> ... key at: [<ffffffff89a5e858>] shmlock_user_lock+0x18/0x5c0
> ... acquired at:
> __raw_spin_lock include/linux/spinlock_api_smp.h:142 [inline]
> _raw_spin_lock+0x2a/0x40 kernel/locking/spinlock.c:151
> spin_lock include/linux/spinlock.h:353 [inline]
> user_shm_lock+0xab/0x230 mm/mlock.c:855
> shmem_lock+0x1dd/0x2d0 mm/shmem.c:2184
> shmctl_do_lock+0x73f/0x8f0 ipc/shm.c:1111
> ksys_shmctl.constprop.0+0x203/0x350 ipc/shm.c:1188
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
> -> (&info->lock){....}-{2:2} {
> INITIAL USE at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irq include/linux/spinlock_api_smp.h:128 [inline]
> _raw_spin_lock_irq+0x5b/0x80 kernel/locking/spinlock.c:167
> spin_lock_irq include/linux/spinlock.h:378 [inline]
> shmem_getpage_gfp+0x937/0x2a10 mm/shmem.c:1882
> shmem_getpage mm/shmem.c:154 [inline]
> shmem_write_begin+0x102/0x1e0 mm/shmem.c:2483
> generic_perform_write+0x20a/0x4e0 mm/filemap.c:3302
> __generic_file_write_iter+0x24c/0x610 mm/filemap.c:3431
> generic_file_write_iter+0x3f3/0x630 mm/filemap.c:3463
> call_write_iter include/linux/fs.h:1907 [inline]
> new_sync_write+0x4a2/0x700 fs/read_write.c:483
> __vfs_write+0xc9/0x100 fs/read_write.c:496
> vfs_write+0x268/0x5d0 fs/read_write.c:558
> ksys_write+0x12d/0x250 fs/read_write.c:611
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> }
> ... key at: [<ffffffff8c667e80>] __key.56422+0x0/0x40
> ... acquired at:
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> shmem_uncharge+0x24/0x270 mm/shmem.c:341
> __split_huge_page mm/huge_memory.c:2613 [inline]
> split_huge_page_to_list+0x274b/0x33b0 mm/huge_memory.c:2886
> split_huge_page include/linux/huge_mm.h:204 [inline]
> shmem_punch_compound+0x13e/0x1e0 mm/shmem.c:814
> shmem_undo_range+0x5f1/0x1b80 mm/shmem.c:870
> shmem_truncate_range+0x27/0xa0 mm/shmem.c:980
> shmem_setattr+0x8b6/0xc80 mm/shmem.c:1039
> notify_change+0xb6d/0x1020 fs/attr.c:336
> do_truncate+0x134/0x1f0 fs/open.c:64
> do_sys_ftruncate+0x4a5/0x570 fs/open.c:195
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
>
>
> stack backtrace:
> CPU: 0 PID: 8337 Comm: syz-executor428 Not tainted 5.6.0-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x188/0x20d lib/dump_stack.c:118
> print_bad_irq_dependency kernel/locking/lockdep.c:2132 [inline]
> check_irq_usage.cold+0x566/0x6de kernel/locking/lockdep.c:2330
> check_prev_add kernel/locking/lockdep.c:2519 [inline]
> check_prevs_add kernel/locking/lockdep.c:2620 [inline]
> validate_chain kernel/locking/lockdep.c:3237 [inline]
> __lock_acquire+0x2c39/0x4e00 kernel/locking/lockdep.c:4344
> lock_acquire+0x1f2/0x8f0 kernel/locking/lockdep.c:4923
> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> shmem_uncharge+0x24/0x270 mm/shmem.c:341
> __split_huge_page mm/huge_memory.c:2613 [inline]
> split_huge_page_to_list+0x274b/0x33b0 mm/huge_memory.c:2886
> split_huge_page include/linux/huge_mm.h:204 [inline]
> shmem_punch_compound+0x13e/0x1e0 mm/shmem.c:814
> shmem_undo_range+0x5f1/0x1b80 mm/shmem.c:870
> shmem_truncate_range+0x27/0xa0 mm/shmem.c:980
> shmem_setattr+0x8b6/0xc80 mm/shmem.c:1039
> notify_change+0xb6d/0x1020 fs/attr.c:336
> do_truncate+0x134/0x1f0 fs/open.c:64
> do_sys_ftruncate+0x4a5/0x570 fs/open.c:195
> do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> entry_SYSCALL_64_after_hwframe+0x49/0xb3
> RIP: 0033:0x44e769
> Code: 4d c9 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 1b c9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> RSP: 002b:00007fe511b3fce8 EFLAGS: 00000246 ORIG_RAX: 000000000000004d
> RAX: ffffffffffffffda RBX: 00000000006e1c68 RCX: 000000000044e769
> RDX: 000000000044e769 RSI: 00000000000001ff RDI: 0000000000000006
> RBP: 00000000006e1c60 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e1c6c
> R13: 00007ffce699f92f R14: 00007fe511b409c0 R15: 0000000000000000
>
>
> ---
> This bug is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>
> syzbot will keep track of this bug report. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> syzbot can test patches for this bug, for details see:
> https://goo.gl/tpsmEJ#testing-patches
>

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