f2fs: fix to use bio_in_atomic() in f2fs_write_end_io()

f2fs_write_end_io() uses in_atomic() to decide whether a write bio which
exceeds max_atc_write_bio_size or max_atc_write_bio_entry_cnt should be
completed in sbi->wq rather than in the current context.

However, in_atomic() is not meant to be used outside core kernel code
(checkpatch.pl warns about it), as it only looks at preempt_count(): it
misses irqs-disabled and RCU read-side critical sections, and on kernels
without CONFIG_PREEMPT_COUNT it cannot see spinlock-held sections at all.
In those contexts, a large write bio will still be completed inline,
which defeats the purpose of the above knobs.

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:

 Context                              | in_atomic()    | bio_in_atomic()
 -------------------------------------+----------------+----------------
 Hard IRQ / softirq                   | true           | true
 IRQs disabled, preempt count 0       | false (missed) | true
 RCU read lock (CONFIG_PREEMPTION)    | false (missed) | true
 Kernel w/o CONFIG_PREEMPT_COUNT      | IRQ ctx only   | always true

Note that on kernels without CONFIG_PREEMPT_COUNT, write bios exceeding
the thresholds will always be offloaded to sbi->wq, since there is no way
to tell whether the current context is atomic. The thresholds default to
UINT_MAX, so the default behavior is not changed.

Cc: stable@kernel.org
Fixes: 3de6b8094115 ("f2fs: Run f2fs_write_end_io() asynchronously")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

0 files changed, 0 insertions, 0 deletions