* [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
@ 2019-11-18 20:15 bugzilla-daemon
2019-11-18 23:08 ` [Bug 205567] " bugzilla-daemon
` (6 more replies)
0 siblings, 7 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-18 20:15 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
Bug ID: 205567
Summary: potential (possibly benign) data race on
ext4_dir_entry_2->inode when getdents64 and rename
happens on the same directory
Product: File System
Version: 2.5
Kernel Version: 5.4-rc5
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: ext4
Assignee: fs_ext4@kernel-bugs.osdl.org
Reporter: mengxu.gatech@gmail.com
Regression: No
I am reporting a potential data race (maybe benign) in the ext4 layer on
ext4_dir_entry_2->inode when getdents64 and rename happens on the same
directory.
[Setup]
mkdir(dir_foo, 0777);
open(dir_foo, 0x10000, 0777) = 0;
dup2(0, 199) = 199;
[Thread 1] getdents64(199, <some buffer>, 4469) = 48;
[Thread 2] rename(dir_foo, aaaaa) = 0;
The function call trace is shown below:
[Thread 1: SYS_getdents64]
__do_sys_getdents64
ksys_getdents64
iterate_dir
ext4_readdir
ext4_dx_readdir
ext4_htree_fill_tree
htree_dirblock_to_tree
[READ] if (de->inode == 0)
[Thread 2: SYS_rename]
__do_renameat2
do_renameat2
vfs_rename
ext4_rename2
ext4_rename
ext4_rename_dir_finish
[WRITE] ent->parent_de->inode = cpu_to_le32(dir_ino);
I could confirm that the WRITE may happen before and after the READ operation
by controlling the timing of the two threads, i.e., by setting breakpoints
before the WRITE statement.
However, I am not very sure about the implication of such a data race (e.g.,
causing violations of assumptions). I would appreciate if you could help check
on this potential bug and advise whether this is a harmful data race or it
is intended. Thank you!
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
@ 2019-11-18 23:08 ` bugzilla-daemon
2019-11-18 23:10 ` bugzilla-daemon
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-18 23:08 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
Eric Sandeen (sandeen@sandeen.net) changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |sandeen@sandeen.net
--- Comment #1 from Eric Sandeen (sandeen@sandeen.net) ---
As a suggestion - if you do not know for sure that these are bugs, it might be
better to ask these questions the list, as opposed to filing bugs.
Is this from code inspection, or are you using KCSAN or a similar tool?
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
2019-11-18 23:08 ` [Bug 205567] " bugzilla-daemon
@ 2019-11-18 23:10 ` bugzilla-daemon
2019-11-18 23:11 ` bugzilla-daemon
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-18 23:10 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
--- Comment #2 from Meng Xu (mengxu.gatech@gmail.com) ---
(In reply to Eric Sandeen from comment #1)
> As a suggestion - if you do not know for sure that these are bugs, it might
> be better to ask these questions the list, as opposed to filing bugs.
>
> Is this from code inspection, or are you using KCSAN or a similar tool?
I am using a tool developed by ourselves, not KCSAN, it is still a work in
progress so it may raise some false positives :(
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
2019-11-18 23:08 ` [Bug 205567] " bugzilla-daemon
2019-11-18 23:10 ` bugzilla-daemon
@ 2019-11-18 23:11 ` bugzilla-daemon
2019-11-19 1:29 ` bugzilla-daemon
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-18 23:11 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
--- Comment #3 from Meng Xu (mengxu.gatech@gmail.com) ---
(In reply to Eric Sandeen from comment #1)
> As a suggestion - if you do not know for sure that these are bugs, it might
> be better to ask these questions the list, as opposed to filing bugs.
>
> Is this from code inspection, or are you using KCSAN or a similar tool?
Thank you for the suggestion, I'll post them to the list then.
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
` (2 preceding siblings ...)
2019-11-18 23:11 ` bugzilla-daemon
@ 2019-11-19 1:29 ` bugzilla-daemon
2019-11-19 1:29 ` bugzilla-daemon
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-19 1:29 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
Theodore Tso (tytso@mit.edu) changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |tytso@mit.edu
--- Comment #4 from Theodore Tso (tytso@mit.edu) ---
POSIX specifically states that it is undefined that if there is a rename taking
place during a readdir() scan, it is undefined whether the entry will appear or
not.
So, not a race.
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
` (3 preceding siblings ...)
2019-11-19 1:29 ` bugzilla-daemon
@ 2019-11-19 1:29 ` bugzilla-daemon
2019-11-19 1:32 ` bugzilla-daemon
2019-11-19 3:03 ` bugzilla-daemon
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-19 1:29 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
--- Comment #5 from Theodore Tso (tytso@mit.edu) ---
(Or rather, it's allowed by the standard, so it's no big deal.)
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
` (4 preceding siblings ...)
2019-11-19 1:29 ` bugzilla-daemon
@ 2019-11-19 1:32 ` bugzilla-daemon
2019-11-19 3:03 ` bugzilla-daemon
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-19 1:32 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
Meng Xu (mengxu.gatech@gmail.com) changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |WILL_NOT_FIX
--- Comment #6 from Meng Xu (mengxu.gatech@gmail.com) ---
(In reply to Theodore Tso from comment #5)
> (Or rather, it's allowed by the standard, so it's no big deal.)
Many thanks for the confirmation Ted!
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* [Bug 205567] potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory
2019-11-18 20:15 [Bug 205567] New: potential (possibly benign) data race on ext4_dir_entry_2->inode when getdents64 and rename happens on the same directory bugzilla-daemon
` (5 preceding siblings ...)
2019-11-19 1:32 ` bugzilla-daemon
@ 2019-11-19 3:03 ` bugzilla-daemon
6 siblings, 0 replies; 8+ messages in thread
From: bugzilla-daemon @ 2019-11-19 3:03 UTC (permalink / raw)
To: linux-ext4
https://bugzilla.kernel.org/show_bug.cgi?id=205567
--- Comment #7 from Meng Xu (mengxu.gatech@gmail.com) ---
(In reply to Theodore Tso from comment #5)
> (Or rather, it's allowed by the standard, so it's no big deal.)
Hi Ted,
Just a quick thought in my mind: do they need to be wrapped with READ_ONCE,
WRITE_ONCE and/or memory barriers so that the visibility of the [WRITE] and all
operations before that [WRITE] are seen by the [READ] and after?
Best Regards,
Meng
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