From: Eric Biggers <ebiggers@kernel.org>
To: linux-cifs@vger.kernel.org
Cc: linux-ext4@vger.kernel.org, syzkaller-bugs@googlegroups.com,
linux-kernel@vger.kernel.org
Subject: [PATCH] cifs: clear PF_MEMALLOC before exiting demultiplex thread
Date: Sat, 7 Mar 2020 20:36:45 -0800 [thread overview]
Message-ID: <20200308043645.1034870-1-ebiggers@kernel.org> (raw)
In-Reply-To: <0000000000000e7156059f751d7b@google.com>
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
next parent reply other threads:[~2020-03-08 4:36 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <0000000000000e7156059f751d7b@google.com>
2020-03-08 4:36 ` Eric Biggers [this message]
2020-03-08 6:16 ` [PATCH v2] cifs: clear PF_MEMALLOC before exiting demultiplex thread 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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