From: Eric Biggers <ebiggers@xxxxxxxxxx> 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@xxxxxxxxxx Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> --- 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
