* [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
end of thread, other threads:[~2020-03-09 5:59 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <0000000000000e7156059f751d7b@google.com> 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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