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Date: Tue, 12 Mar 2019 19:14:52 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, chao@...nel.org
Subject: Re: [PATCH] f2fs: fix to avoid deadlock in f2fs_read_inline_dir()
On 03/13, Chao Yu wrote:
> On 2019/3/13 4:09, Jaegeuk Kim wrote:
> > On 03/12, Chao Yu wrote:
> >> As Jiqun Li reported in bugzilla:
> >>
> >> https://bugzilla.kernel.org/show_bug.cgi?id=202883
> >>
> >> sometimes, dead lock when make system call SYS_getdents64 with fsync() is
> >> called by another process.
> >>
> >> monkey running on android9.0
> >>
> >> 1. task 9785 held sbi->cp_rwsem and waiting lock_page()
> >> 2. task 10349 held mm_sem and waiting sbi->cp_rwsem
> >> 3. task 9709 held lock_page() and waiting mm_sem
> >>
> >> so this is a dead lock scenario.
> >>
> >> task stack is show by crash tools as following
> >>
> >> crash_arm64> bt ffffffc03c354080
> >> PID: 9785 TASK: ffffffc03c354080 CPU: 1 COMMAND: "RxIoScheduler-3"
> >>>> #7 [ffffffc01b50fac0] __lock_page at ffffff80081b11e8
> >>
> >> crash-arm64> bt 10349
> >> PID: 10349 TASK: ffffffc018b83080 CPU: 1 COMMAND: "BUGLY_ASYNC_UPL"
> >>>> #3 [ffffffc01f8cfa40] rwsem_down_read_failed at ffffff8008a93afc
> >> PC: 00000033 LR: 00000000 SP: 00000000 PSTATE: ffffffffffffffff
> >>
> >> crash-arm64> bt 9709
> >> PID: 9709 TASK: ffffffc03e7f3080 CPU: 1 COMMAND: "IntentService[A"
> >>>> #3 [ffffffc001e67850] rwsem_down_read_failed at ffffff8008a93afc
> >>>> #8 [ffffffc001e67b80] el1_ia at ffffff8008084fc4
> >> PC: ffffff8008274114 [compat_filldir64+120]
> >> LR: ffffff80083584d4 [f2fs_fill_dentries+448]
> >> SP: ffffffc001e67b80 PSTATE: 80400145
> >> X29: ffffffc001e67b80 X28: 0000000000000000 X27: 000000000000001a
> >> X26: 00000000000093d7 X25: ffffffc070d52480 X24: 0000000000000008
> >> X23: 0000000000000028 X22: 00000000d43dfd60 X21: ffffffc001e67e90
> >> X20: 0000000000000011 X19: ffffff80093a4000 X18: 0000000000000000
> >> X17: 0000000000000000 X16: 0000000000000000 X15: 0000000000000000
> >> X14: ffffffffffffffff X13: 0000000000000008 X12: 0101010101010101
> >> X11: 7f7f7f7f7f7f7f7f X10: 6a6a6a6a6a6a6a6a X9: 7f7f7f7f7f7f7f7f
> >> X8: 0000000080808000 X7: ffffff800827409c X6: 0000000080808000
> >> X5: 0000000000000008 X4: 00000000000093d7 X3: 000000000000001a
> >> X2: 0000000000000011 X1: ffffffc070d52480 X0: 0000000000800238
> >>>> #9 [ffffffc001e67be0] f2fs_fill_dentries at ffffff80083584d0
> >> PC: 0000003c LR: 00000000 SP: 00000000 PSTATE: 000000d9
> >> X12: f48a02ff X11: d4678960 X10: d43dfc00 X9: d4678ae4
> >> X8: 00000058 X7: d4678994 X6: d43de800 X5: 000000d9
> >> X4: d43dfc0c X3: d43dfc10 X2: d46799c8 X1: 00000000
> >> X0: 00001068
> >>
> >> Below potential deadlock will happen between three threads:
> >> Thread A Thread B Thread C
> >> - f2fs_do_sync_file
> >> - f2fs_write_checkpoint
> >> - down_write(&sbi->node_change) -- 1)
> >> - do_page_fault
> >> - down_write(&mm->mmap_sem) -- 2)
> >> - do_wp_page
> >> - f2fs_vm_page_mkwrite
> >> - getdents64
> >> - f2fs_read_inline_dir
> >> - lock_page -- 3)
> >> - f2fs_sync_node_pages
> >> - lock_page -- 3)
> >> - __do_map_lock
> >> - down_read(&sbi->node_change) -- 1)
> >> - f2fs_fill_dentries
> >> - dir_emit
> >> - compat_filldir64
> >> - do_page_fault
> >> - down_read(&mm->mmap_sem) -- 2)
> >>
> >> Since f2fs_readdir is protected by inode.i_rwsem, there should not be
> >
> > Well, what about other dir operations which can convert inline_dentry?
>
> All those operations which can add/update/delete dents will be covered with
> down_write(inode.i_rwsem), so we are safe.
Okay.
>
> > How about allocating a buffer shortly like this?
>
> If there is no race, allocating additional memory to store instantaneous
> dents is unnecessary? How do you think?
If we're really safe with i_rwsem, it's fine.
>
> Thanks
>
> >
> > ---
> > fs/f2fs/inline.c | 20 ++++++++++++++------
> > 1 file changed, 14 insertions(+), 6 deletions(-)
> >
> > diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> > index a1381d05956b..50a946d55778 100644
> > --- a/fs/f2fs/inline.c
> > +++ b/fs/f2fs/inline.c
> > @@ -647,12 +647,10 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
> > struct inode *inode = file_inode(file);
> > struct page *ipage = NULL;
> > struct f2fs_dentry_ptr d;
> > - void *inline_dentry = NULL;
> > + void *inline_dentry = NULL, *buf = NULL;
> > int err;
> >
> > - make_dentry_ptr_inline(inode, &d, inline_dentry);
> > -
> > - if (ctx->pos == d.max)
> > + if (ctx->pos >= NR_INLINE_DENTRY(inode))
> > return 0;
> >
> > ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
> > @@ -660,14 +658,24 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
> > return PTR_ERR(ipage);
> >
> > inline_dentry = inline_data_addr(inode, ipage);
> > + buf = f2fs_kmalloc(F2FS_I_SB(inode),
> > + MAX_INLINE_DATA(inode), GFP_F2FS_ZERO);
> > + if (!buf) {
> > + f2fs_put_page(ipage, 1);
> > + err = -ENOMEM;
> > + goto out;
> > + }
> > + memcpy(buf, inline_dentry, MAX_INLINE_DATA(inode));
> > + make_dentry_ptr_inline(inode, &d, buf);
> >
> > - make_dentry_ptr_inline(inode, &d, inline_dentry);
> > + f2fs_put_page(ipage, 1);
> >
> > err = f2fs_fill_dentries(ctx, &d, 0, fstr);
> > if (!err)
> > ctx->pos = d.max;
> >
> > - f2fs_put_page(ipage, 1);
> > + kvfree(buf);
> > +out:
> > return err < 0 ? err : 0;
> > }
> >
> >
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