FAILED: patch "[PATCH] f2fs: fix to use bio_in_atomic() in f2fs_read_end_io()" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] f2fs: fix to use bio_in_atomic() in f2fs_read_end_io()" failed to apply to 6.6-stable tree

[Sasha Levin]

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x a605d5d71a6d280c43c7ede9778dda63fb5c3f22
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '20261107053451-failed-6.6-a605d5d71a6d@kernel.org' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Thanks,
Sasha

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

From a605d5d71a6d280c43c7ede9778dda63fb5c3f22 Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@kernel.org>
Date: Sat, 10 Oct 2026 14:55:46 +0800
Subject: [PATCH] f2fs: fix to use bio_in_atomic() in f2fs_read_end_io()

f2fs_read_end_io() uses "in_task() && !irqs_disabled()" to decide
whether it is safe to sleep, the result is passed down as @in_task to:
- f2fs_put_dic() -> f2fs_free_dic() -> f2fs_release_decomp_mem()
  -> vm_unmap_ram(), which may sleep.
- f2fs_end_read_compressed_page() -> f2fs_cache_compressed_page()
  -> f2fs_grab_cache() -> f2fs_lock_cache(), which may sleep in
  wait_on_bit_lock().

However, the check still treats below task contexts as sleepable:
- with spinlock held via spin_lock(), i.e. preempt count != 0 while
  irqs are enabled.
- with BH disabled via local_bh_disable().
- inside an RCU read lock on kernels with CONFIG_PREEMPTION.
- with any spinlock held on kernels without CONFIG_PREEMPT_COUNT.

So the "sleeping function called from invalid context" issue fixed by
commit 08a7efc5b02a ("f2fs: vm_unmap_ram() may be called from an
invalid context") can still be triggered.

The block layer provides bio_in_atomic() for exactly this purpose, it
checks rcu_preempt_depth() and preemptible(), and conservatively returns
true if CONFIG_PREEMPT_COUNT is disabled, let's use it instead. The
difference is as below:

 old: intask = in_task() && !irqs_disabled()
 new: intask = !bio_in_atomic()

 Context                              | old intask     | new intask
 -------------------------------------+----------------+----------------
 Hard IRQ / softirq                   | false          | false
 IRQs disabled                        | false          | false
 spin_lock() held, IRQs enabled       | true (wrong)   | false
 BH disabled by local_bh_disable()    | true (wrong)   | false
 RCU read lock (CONFIG_PREEMPTION)    | true (wrong)   | false
 Spinlock held, w/o PREEMPT_COUNT     | true (wrong)   | false

Note that on kernels without CONFIG_PREEMPT_COUNT, bio_in_atomic()
always returns true, so dic freeing will always be offloaded to sbi->wq,
and compressed pages will not be cached in f2fs_read_end_io(); this is
the price of correctness, since there is no way to tell whether the
current context can sleep.

Cc: stable@kernel.org
Fixes: 08a7efc5b02a ("f2fs: vm_unmap_ram() may be called from an invalid context")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 fs/f2fs/data.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index ae3bde0767f3c..a8d39add5cbe0 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -271,7 +271,7 @@ static void f2fs_read_end_io(struct bio *bio)
 {
 	struct f2fs_sb_info *sbi = F2FS_F_SB(bio_first_folio_all(bio));
 	struct bio_post_read_ctx *ctx;
-	bool intask = in_task() && !irqs_disabled();
+	bool intask = !bio_in_atomic();
 
 	iostat_update_and_unbind_ctx(bio);
 	ctx = bio->bi_private;
-- 
2.53.0

[PATCH 6.6.y 1/2] block: introduce bio_in_atomic()

[Sasha Levin]

From: Tal Zussman <tz2294@columbia.edu>

[ Upstream commit 8ed0831b5263e1aa48d99063795a1f20e4e69b50 ]

Move the atomic context detection logic from erofs's z_erofs_in_atomic()
into the block layer as bio_in_atomic(). This helper returns true when
the current context is unsafe for sleeping bio completion handlers (e.g.,
hard/soft IRQ, preempt-disabled).

The logic was originally added to erofs in commit c99fab6e80b7 ("erofs:
fix atomic context detection when !CONFIG_DEBUG_LOCK_ALLOC"). A
subsequent patch will use it in the block layer's bio completion
infrastructure, so move it to include/linux/bio.h where both subsystems
can share it.

Convert erofs to call the new bio_in_atomic() directly.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260730-blk-dontcache-v7-1-3e8e6850068d@columbia.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: a605d5d71a6d ("f2fs: fix to use bio_in_atomic() in f2fs_read_end_io()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/erofs/zdata.c    | 11 +----------
 include/linux/bio.h | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 10 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index ede86dd93b5dd..1a8c4a068db8e 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1404,15 +1404,6 @@ static void z_erofs_decompressqueue_kthread_work(struct kthread_work *work)
 }
 #endif
 
-/* Use (kthread_)work in atomic contexts to minimize scheduling overhead */
-static inline bool z_erofs_in_atomic(void)
-{
-	if (IS_ENABLED(CONFIG_PREEMPTION) && rcu_preempt_depth())
-		return true;
-	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
-		return true;
-	return !preemptible();
-}
 
 static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 				       int bios)
@@ -1429,7 +1420,7 @@ static void z_erofs_decompress_kickoff(struct z_erofs_decompressqueue *io,
 
 	if (atomic_add_return(bios, &io->pending_bios))
 		return;
-	if (z_erofs_in_atomic()) {
+	if (bio_in_atomic()) {
 		/* See `sync_decompress` in sysfs-fs-erofs for more details */
 		if (sbi->opt.sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO)
 			sbi->opt.sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON;
diff --git a/include/linux/bio.h b/include/linux/bio.h
index f193aef4fac08..089008d1d21ef 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -438,6 +438,21 @@ static inline struct bio *bio_alloc(struct block_device *bdev,
 
 void submit_bio(struct bio *bio);
 
+/**
+ * bio_in_atomic - check if the current context is unsafe for bio completion
+ *
+ * Return: %true in atomic contexts (e.g. hard/soft IRQ, preempt-disabled);
+ * %false when a bio can be safely completed in the current context.
+ */
+static inline bool bio_in_atomic(void)
+{
+	if (IS_ENABLED(CONFIG_PREEMPTION) && rcu_preempt_depth())
+		return true;
+	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		return true;
+	return !preemptible();
+}
+
 extern void bio_endio(struct bio *);
 
 static inline void bio_io_error(struct bio *bio)
-- 
2.53.0

[PATCH 6.6.y 2/2] f2fs: fix to use bio_in_atomic() in f2fs_read_end_io()

[Sasha Levin]

From: Chao Yu <chao@kernel.org>

[ Upstream commit a605d5d71a6d280c43c7ede9778dda63fb5c3f22 ]

f2fs_read_end_io() uses "in_task() && !irqs_disabled()" to decide
whether it is safe to sleep, the result is passed down as @in_task to:
- f2fs_put_dic() -> f2fs_free_dic() -> f2fs_release_decomp_mem()
  -> vm_unmap_ram(), which may sleep.
- f2fs_end_read_compressed_page() -> f2fs_cache_compressed_page()
  -> f2fs_grab_cache() -> f2fs_lock_cache(), which may sleep in
  wait_on_bit_lock().

However, the check still treats below task contexts as sleepable:
- with spinlock held via spin_lock(), i.e. preempt count != 0 while
  irqs are enabled.
- with BH disabled via local_bh_disable().
- inside an RCU read lock on kernels with CONFIG_PREEMPTION.
- with any spinlock held on kernels without CONFIG_PREEMPT_COUNT.

So the "sleeping function called from invalid context" issue fixed by
commit 08a7efc5b02a ("f2fs: vm_unmap_ram() may be called from an
invalid context") can still be triggered.

The block layer provides bio_in_atomic() for exactly this purpose, it
checks rcu_preempt_depth() and preemptible(), and conservatively returns
true if CONFIG_PREEMPT_COUNT is disabled, let's use it instead. The
difference is as below:

 old: intask = in_task() && !irqs_disabled()
 new: intask = !bio_in_atomic()

 Context                              | old intask     | new intask
 -------------------------------------+----------------+----------------
 Hard IRQ / softirq                   | false          | false
 IRQs disabled                        | false          | false
 spin_lock() held, IRQs enabled       | true (wrong)   | false
 BH disabled by local_bh_disable()    | true (wrong)   | false
 RCU read lock (CONFIG_PREEMPTION)    | true (wrong)   | false
 Spinlock held, w/o PREEMPT_COUNT     | true (wrong)   | false

Note that on kernels without CONFIG_PREEMPT_COUNT, bio_in_atomic()
always returns true, so dic freeing will always be offloaded to sbi->wq,
and compressed pages will not be cached in f2fs_read_end_io(); this is
the price of correctness, since there is no way to tell whether the
current context can sleep.

Cc: stable@kernel.org
Fixes: 08a7efc5b02a ("f2fs: vm_unmap_ram() may be called from an invalid context")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/f2fs/data.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index b0c633c5deb75..f3992a728de69 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -288,7 +288,7 @@ static void f2fs_read_end_io(struct bio *bio)
 {
 	struct f2fs_sb_info *sbi = F2FS_P_SB(bio_first_page_all(bio));
 	struct bio_post_read_ctx *ctx;
-	bool intask = in_task() && !irqs_disabled();
+	bool intask = !bio_in_atomic();
 
 	iostat_update_and_unbind_ctx(bio);
 	ctx = bio->bi_private;
-- 
2.53.0