FAILED: patch "[PATCH] mm/page_alloc: fix potential deadlock on zonelist_update_seq" failed to apply to 4.19-stable tree

FAILED: patch "[PATCH] mm/page_alloc: fix potential deadlock on zonelist_update_seq" failed to apply to 4.19-stable tree

[gregkh]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y
git checkout FETCH_HEAD
git cherry-pick -x 1007843a91909a4995ee78a538f62d8665705b66
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2023042452-stopper-engross-e9da@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

1007843a9190 ("mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock")
3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 1007843a91909a4995ee78a538f62d8665705b66 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Tue, 4 Apr 2023 23:31:58 +0900
Subject: [PATCH] mm/page_alloc: fix potential deadlock on zonelist_update_seq
 seqlock
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

syzbot is reporting circular locking dependency which involves
zonelist_update_seq seqlock [1], for this lock is checked by memory
allocation requests which do not need to be retried.

One deadlock scenario is kmalloc(GFP_ATOMIC) from an interrupt handler.

  CPU0
  ----
  __build_all_zonelists() {
    write_seqlock(&zonelist_update_seq); // makes zonelist_update_seq.seqcount odd
    // e.g. timer interrupt handler runs at this moment
      some_timer_func() {
        kmalloc(GFP_ATOMIC) {
          __alloc_pages_slowpath() {
            read_seqbegin(&zonelist_update_seq) {
              // spins forever because zonelist_update_seq.seqcount is odd
            }
          }
        }
      }
    // e.g. timer interrupt handler finishes
    write_sequnlock(&zonelist_update_seq); // makes zonelist_update_seq.seqcount even
  }

This deadlock scenario can be easily eliminated by not calling
read_seqbegin(&zonelist_update_seq) from !__GFP_DIRECT_RECLAIM allocation
requests, for retry is applicable to only __GFP_DIRECT_RECLAIM allocation
requests.  But Michal Hocko does not know whether we should go with this
approach.

Another deadlock scenario which syzbot is reporting is a race between
kmalloc(GFP_ATOMIC) from tty_insert_flip_string_and_push_buffer() with
port->lock held and printk() from __build_all_zonelists() with
zonelist_update_seq held.

  CPU0                                   CPU1
  ----                                   ----
  pty_write() {
    tty_insert_flip_string_and_push_buffer() {
                                         __build_all_zonelists() {
                                           write_seqlock(&zonelist_update_seq);
                                           build_zonelists() {
                                             printk() {
                                               vprintk() {
                                                 vprintk_default() {
                                                   vprintk_emit() {
                                                     console_unlock() {
                                                       console_flush_all() {
                                                         console_emit_next_record() {
                                                           con->write() = serial8250_console_write() {
      spin_lock_irqsave(&port->lock, flags);
      tty_insert_flip_string() {
        tty_insert_flip_string_fixed_flag() {
          __tty_buffer_request_room() {
            tty_buffer_alloc() {
              kmalloc(GFP_ATOMIC | __GFP_NOWARN) {
                __alloc_pages_slowpath() {
                  zonelist_iter_begin() {
                    read_seqbegin(&zonelist_update_seq); // spins forever because zonelist_update_seq.seqcount is odd
                                                             spin_lock_irqsave(&port->lock, flags); // spins forever because port->lock is held
                    }
                  }
                }
              }
            }
          }
        }
      }
      spin_unlock_irqrestore(&port->lock, flags);
                                                             // message is printed to console
                                                             spin_unlock_irqrestore(&port->lock, flags);
                                                           }
                                                         }
                                                       }
                                                     }
                                                   }
                                                 }
                                               }
                                             }
                                           }
                                           write_sequnlock(&zonelist_update_seq);
                                         }
    }
  }

This deadlock scenario can be eliminated by

  preventing interrupt context from calling kmalloc(GFP_ATOMIC)

and

  preventing printk() from calling console_flush_all()

while zonelist_update_seq.seqcount is odd.

Since Petr Mladek thinks that __build_all_zonelists() can become a
candidate for deferring printk() [2], let's address this problem by

  disabling local interrupts in order to avoid kmalloc(GFP_ATOMIC)

and

  disabling synchronous printk() in order to avoid console_flush_all()

.

As a side effect of minimizing duration of zonelist_update_seq.seqcount
being odd by disabling synchronous printk(), latency at
read_seqbegin(&zonelist_update_seq) for both !__GFP_DIRECT_RECLAIM and
__GFP_DIRECT_RECLAIM allocation requests will be reduced.  Although, from
lockdep perspective, not calling read_seqbegin(&zonelist_update_seq) (i.e.
do not record unnecessary locking dependency) from interrupt context is
still preferable, even if we don't allow calling kmalloc(GFP_ATOMIC)
inside
write_seqlock(&zonelist_update_seq)/write_sequnlock(&zonelist_update_seq)
section...

Link: https://lkml.kernel.org/r/8796b95c-3da3-5885-fddd-6ef55f30e4d3@I-love.SAKURA.ne.jp
Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation")
Link: https://lkml.kernel.org/r/ZCrs+1cDqPWTDFNM@alley [2]
Reported-by: syzbot <syzbot+223c7461c58c58a4cb10@syzkaller.appspotmail.com>
  Link: https://syzkaller.appspot.com/bug?extid=223c7461c58c58a4cb10 [1]
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Cc: Petr Mladek <pmladek@suse.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: Patrick Daly <quic_pdaly@quicinc.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7136c36c5d01..e8b4f294d763 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6632,7 +6632,21 @@ static void __build_all_zonelists(void *data)
 	int nid;
 	int __maybe_unused cpu;
 	pg_data_t *self = data;
+	unsigned long flags;
 
+	/*
+	 * Explicitly disable this CPU's interrupts before taking seqlock
+	 * to prevent any IRQ handler from calling into the page allocator
+	 * (e.g. GFP_ATOMIC) that could hit zonelist_iter_begin and livelock.
+	 */
+	local_irq_save(flags);
+	/*
+	 * Explicitly disable this CPU's synchronous printk() before taking
+	 * seqlock to prevent any printk() from trying to hold port->lock, for
+	 * tty_insert_flip_string_and_push_buffer() on other CPU might be
+	 * calling kmalloc(GFP_ATOMIC | __GFP_NOWARN) with port->lock held.
+	 */
+	printk_deferred_enter();
 	write_seqlock(&zonelist_update_seq);
 
 #ifdef CONFIG_NUMA
@@ -6671,6 +6685,8 @@ static void __build_all_zonelists(void *data)
 	}
 
 	write_sequnlock(&zonelist_update_seq);
+	printk_deferred_exit();
+	local_irq_restore(flags);
 }
 
 static noinline void __init

[PATCH 4.19.y] printk: declare printk_deferred_{enter,safe}() in include/linux/printk.h

[Tetsuo Handa]

commit 85e3e7fbbb720b9897fba9a99659e31cbd1c082e upstream.

[This patch implements subset of original commit 85e3e7fbbb72 ("printk:
remove NMI tracking") where commit 1007843a9190 ("mm/page_alloc: fix
potential deadlock on zonelist_update_seq seqlock") depends on, for
commit 3d36424b3b58 ("mm/page_alloc: fix race condition between
build_all_zonelists and page allocation") was backported to stable.]

All NMI contexts are handled the same as the safe context: store the
message and defer printing. There is no need to have special NMI
context tracking for this. Using in_nmi() is enough.

There are several parts of the kernel that are manually calling into
the printk NMI context tracking in order to cause general printk
deferred printing:

    arch/arm/kernel/smp.c
    arch/powerpc/kexec/crash.c
    kernel/trace/trace.c

For arm/kernel/smp.c and powerpc/kexec/crash.c, provide a new
function pair printk_deferred_enter/exit that explicitly achieves the
same objective.

For ftrace, remove the printk context manipulation completely. It was
added in commit 03fc7f9c99c1 ("printk/nmi: Prevent deadlock when
accessing the main log buffer in NMI"). The purpose was to enforce
storing messages directly into the ring buffer even in NMI context.
It really should have only modified the behavior in NMI context.
There is no need for a special behavior any longer. All messages are
always stored directly now. The console deferring is handled
transparently in vprintk().

Signed-off-by: John Ogness <john.ogness@linutronix.de>
[pmladek@suse.com: Remove special handling in ftrace.c completely.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210715193359.25946-5-john.ogness@linutronix.de
[penguin-kernel: Copy only printk_deferred_{enter,safe}() definition ]
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
 include/linux/printk.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 6dd867e39365..f4d7e643f010 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -525,4 +525,23 @@ static inline void print_hex_dump_debug(const char *prefix_str, int prefix_type,
 }
 #endif
 
+#ifdef CONFIG_PRINTK
+extern void __printk_safe_enter(void);
+extern void __printk_safe_exit(void);
+/*
+ * The printk_deferred_enter/exit macros are available only as a hack for
+ * some code paths that need to defer all printk console printing. Interrupts
+ * must be disabled for the deferred duration.
+ */
+#define printk_deferred_enter __printk_safe_enter
+#define printk_deferred_exit __printk_safe_exit
+#else
+static inline void printk_deferred_enter(void)
+{
+}
+static inline void printk_deferred_exit(void)
+{
+}
+#endif
+
 #endif
-- 
2.34.1