* [PATCH] cifs: clear PF_MEMALLOC before exiting demultiplex thread
[not found] <0000000000000e7156059f751d7b@google.com>
@ 2020-03-08 4:36 ` Eric Biggers
2020-03-08 6:16 ` [PATCH v2] " Eric Biggers
0 siblings, 1 reply; 5+ messages in thread
From: Eric Biggers @ 2020-03-08 4:36 UTC (permalink / raw)
To: linux-cifs; +Cc: linux-ext4, syzkaller-bugs, linux-kernel
From: Eric Biggers <ebiggers@google.com>
Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set
during do_exit(). That can confuse things. For example, if BSD process
accounting is enabled, then it's possible for do_exit() to end up
calling ext4_write_inode(). That triggers the
WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes
(appropriately) that inodes aren't written when allocating memory.
This case was reported by syzbot at
https://lkml.kernel.org/r/0000000000000e7156059f751d7b@google.com.
Fix this in cifs_demultiplex_thread() by using the helper functions to
save and restore PF_MEMALLOC.
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/cifs/connect.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 4804d1df8c1c..beab1dc2dc01 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -1164,8 +1164,9 @@ cifs_demultiplex_thread(void *p)
struct task_struct *task_to_wake = NULL;
struct mid_q_entry *mids[MAX_COMPOUND];
char *bufs[MAX_COMPOUND];
+ unsigned int noreclaim_flag;
- current->flags |= PF_MEMALLOC;
+ noreclaim_flag = memalloc_noreclaim_save();
cifs_dbg(FYI, "Demultiplex PID: %d\n", task_pid_nr(current));
length = atomic_inc_return(&tcpSesAllocCount);
@@ -1320,6 +1321,7 @@ cifs_demultiplex_thread(void *p)
set_current_state(TASK_RUNNING);
}
+ memalloc_noreclaim_restore(noreclaim_flag);
module_put_and_exit(0);
}
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v2] cifs: clear PF_MEMALLOC before exiting demultiplex thread
2020-03-08 4:36 ` [PATCH] cifs: clear PF_MEMALLOC before exiting demultiplex thread Eric Biggers
@ 2020-03-08 6:16 ` Eric Biggers
2020-03-08 18:43 ` Steve French
0 siblings, 1 reply; 5+ messages in thread
From: Eric Biggers @ 2020-03-08 6:16 UTC (permalink / raw)
To: linux-cifs; +Cc: linux-ext4, syzkaller-bugs, linux-kernel
From: Eric Biggers <ebiggers@google.com>
Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set
during do_exit(). That can confuse things. For example, if BSD process
accounting is enabled, then it's possible for do_exit() to end up
calling ext4_write_inode(). That triggers the
WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes
(appropriately) that inodes aren't written when allocating memory.
This case was reported by syzbot at
https://lkml.kernel.org/r/0000000000000e7156059f751d7b@google.com.
Fix this in cifs_demultiplex_thread() by using the helper functions to
save and restore PF_MEMALLOC.
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
v2: added missing include of <linux/sched/mm.h>
(I missed that I didn't actually have CONFIG_CIFS set...)
fs/cifs/connect.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 4804d1df8c1c..97b8eb585cf9 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -21,6 +21,7 @@
#include <linux/fs.h>
#include <linux/net.h>
#include <linux/string.h>
+#include <linux/sched/mm.h>
#include <linux/sched/signal.h>
#include <linux/list.h>
#include <linux/wait.h>
@@ -1164,8 +1165,9 @@ cifs_demultiplex_thread(void *p)
struct task_struct *task_to_wake = NULL;
struct mid_q_entry *mids[MAX_COMPOUND];
char *bufs[MAX_COMPOUND];
+ unsigned int noreclaim_flag;
- current->flags |= PF_MEMALLOC;
+ noreclaim_flag = memalloc_noreclaim_save();
cifs_dbg(FYI, "Demultiplex PID: %d\n", task_pid_nr(current));
length = atomic_inc_return(&tcpSesAllocCount);
@@ -1320,6 +1322,7 @@ cifs_demultiplex_thread(void *p)
set_current_state(TASK_RUNNING);
}
+ memalloc_noreclaim_restore(noreclaim_flag);
module_put_and_exit(0);
}
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] cifs: clear PF_MEMALLOC before exiting demultiplex thread
2020-03-08 6:16 ` [PATCH v2] " Eric Biggers
@ 2020-03-08 18:43 ` Steve French
2020-03-09 5:56 ` Eric Biggers
0 siblings, 1 reply; 5+ messages in thread
From: Steve French @ 2020-03-08 18:43 UTC (permalink / raw)
To: Eric Biggers; +Cc: CIFS, linux-ext4, syzkaller-bugs, LKML
merged into cifs-2.6.git for-next
running buildbot cifs/smb3 automated regression tests now
On Sun, Mar 8, 2020 at 12:17 AM Eric Biggers <ebiggers@kernel.org> wrote:
>
> From: Eric Biggers <ebiggers@google.com>
>
> Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set
> during do_exit(). That can confuse things. For example, if BSD process
> accounting is enabled, then it's possible for do_exit() to end up
> calling ext4_write_inode(). That triggers the
> WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes
> (appropriately) that inodes aren't written when allocating memory.
>
> This case was reported by syzbot at
> https://lkml.kernel.org/r/0000000000000e7156059f751d7b@google.com.
>
> Fix this in cifs_demultiplex_thread() by using the helper functions to
> save and restore PF_MEMALLOC.
>
> Signed-off-by: Eric Biggers <ebiggers@google.com>
> ---
>
> v2: added missing include of <linux/sched/mm.h>
> (I missed that I didn't actually have CONFIG_CIFS set...)
>
> fs/cifs/connect.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
> index 4804d1df8c1c..97b8eb585cf9 100644
> --- a/fs/cifs/connect.c
> +++ b/fs/cifs/connect.c
> @@ -21,6 +21,7 @@
> #include <linux/fs.h>
> #include <linux/net.h>
> #include <linux/string.h>
> +#include <linux/sched/mm.h>
> #include <linux/sched/signal.h>
> #include <linux/list.h>
> #include <linux/wait.h>
> @@ -1164,8 +1165,9 @@ cifs_demultiplex_thread(void *p)
> struct task_struct *task_to_wake = NULL;
> struct mid_q_entry *mids[MAX_COMPOUND];
> char *bufs[MAX_COMPOUND];
> + unsigned int noreclaim_flag;
>
> - current->flags |= PF_MEMALLOC;
> + noreclaim_flag = memalloc_noreclaim_save();
> cifs_dbg(FYI, "Demultiplex PID: %d\n", task_pid_nr(current));
>
> length = atomic_inc_return(&tcpSesAllocCount);
> @@ -1320,6 +1322,7 @@ cifs_demultiplex_thread(void *p)
> set_current_state(TASK_RUNNING);
> }
>
> + memalloc_noreclaim_restore(noreclaim_flag);
> module_put_and_exit(0);
> }
>
> --
> 2.25.1
>
--
Thanks,
Steve
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] cifs: clear PF_MEMALLOC before exiting demultiplex thread
2020-03-08 18:43 ` Steve French
@ 2020-03-09 5:56 ` Eric Biggers
2020-03-09 5:58 ` [PATCH v3] " Eric Biggers
0 siblings, 1 reply; 5+ messages in thread
From: Eric Biggers @ 2020-03-09 5:56 UTC (permalink / raw)
To: Steve French; +Cc: CIFS, linux-ext4, syzkaller-bugs, LKML
On Sun, Mar 08, 2020 at 01:43:56PM -0500, Steve French wrote:
> merged into cifs-2.6.git for-next
>
> running buildbot cifs/smb3 automated regression tests now
>
Thanks. FYI, I also sent a similar patch for an XFS kernel thread, and the XFS
folks requested more details in the commit message [1]. So I ended up trying to
reproduce this warning on both XFS and CIFS, and I added more details to both
commit messages. So if it's not too late, please update the CIFS commit to the
v3 I'm sending out. Thanks!
[1] https://lkml.kernel.org/linux-xfs/20200308230307.GM10776@dread.disaster.area
- Eric
^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH v3] cifs: clear PF_MEMALLOC before exiting demultiplex thread
2020-03-09 5:56 ` Eric Biggers
@ 2020-03-09 5:58 ` Eric Biggers
0 siblings, 0 replies; 5+ messages in thread
From: Eric Biggers @ 2020-03-09 5:58 UTC (permalink / raw)
To: linux-cifs; +Cc: linux-ext4, syzkaller-bugs, linux-kernel
From: Eric Biggers <ebiggers@google.com>
Leaving PF_MEMALLOC set when exiting a kthread causes it to remain set
during do_exit(). That can confuse things. For example, if BSD process
accounting is enabled and the accounting file has FS_SYNC_FL set and is
located on an ext4 filesystem without a journal, then do_exit() can end
up calling ext4_write_inode(). That triggers the
WARN_ON_ONCE(current->flags & PF_MEMALLOC) there, as it assumes
(appropriately) that inodes aren't written when allocating memory.
This was originally reported for another kernel thread, xfsaild() [1].
cifs_demultiplex_thread() also exits with PF_MEMALLOC set, so it's
potentially subject to this same class of issue -- though I haven't been
able to reproduce the WARN_ON_ONCE() via CIFS, since unlike xfsaild(),
cifs_demultiplex_thread() is sent SIGKILL before exiting, and that
interrupts the write to the BSD process accounting file.
Either way, leaving PF_MEMALLOC set is potentially problematic. Let's
clean this up by properly saving and restoring PF_MEMALLOC.
[1] https://lore.kernel.org/r/0000000000000e7156059f751d7b@google.com
Signed-off-by: Eric Biggers <ebiggers@google.com>
---
v3: improved commit message
v2: added missing include
fs/cifs/connect.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/cifs/connect.c b/fs/cifs/connect.c
index 4804d1df8c1cf..97b8eb585cf9d 100644
--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -21,6 +21,7 @@
#include <linux/fs.h>
#include <linux/net.h>
#include <linux/string.h>
+#include <linux/sched/mm.h>
#include <linux/sched/signal.h>
#include <linux/list.h>
#include <linux/wait.h>
@@ -1164,8 +1165,9 @@ cifs_demultiplex_thread(void *p)
struct task_struct *task_to_wake = NULL;
struct mid_q_entry *mids[MAX_COMPOUND];
char *bufs[MAX_COMPOUND];
+ unsigned int noreclaim_flag;
- current->flags |= PF_MEMALLOC;
+ noreclaim_flag = memalloc_noreclaim_save();
cifs_dbg(FYI, "Demultiplex PID: %d\n", task_pid_nr(current));
length = atomic_inc_return(&tcpSesAllocCount);
@@ -1320,6 +1322,7 @@ cifs_demultiplex_thread(void *p)
set_current_state(TASK_RUNNING);
}
+ memalloc_noreclaim_restore(noreclaim_flag);
module_put_and_exit(0);
}
--
2.25.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
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2020-03-08 4:36 ` [PATCH] cifs: clear PF_MEMALLOC before exiting demultiplex thread Eric Biggers
2020-03-08 6:16 ` [PATCH v2] " Eric Biggers
2020-03-08 18:43 ` Steve French
2020-03-09 5:56 ` Eric Biggers
2020-03-09 5:58 ` [PATCH v3] " Eric Biggers
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