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SubjectRe: [f2fs-dev] [PATCH] f2fs: do not use mutex lock in atomic context
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On 2/14/2019 9:40 PM, Chao Yu wrote:
> On 2019-2-14 15:46, Sahitya Tummala wrote:
>> On Wed, Feb 13, 2019 at 11:25:31AM +0800, Chao Yu wrote:
>>> On 2019/2/4 16:06, Sahitya Tummala wrote:
>>>> Fix below warning coming because of using mutex lock in atomic context.
>>>>
>>>> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:98
>>>> in_atomic(): 1, irqs_disabled(): 0, pid: 585, name: sh
>>>> Preemption disabled at: __radix_tree_preload+0x28/0x130
>>>> Call trace:
>>>> dump_backtrace+0x0/0x2b4
>>>> show_stack+0x20/0x28
>>>> dump_stack+0xa8/0xe0
>>>> ___might_sleep+0x144/0x194
>>>> __might_sleep+0x58/0x8c
>>>> mutex_lock+0x2c/0x48
>>>> f2fs_trace_pid+0x88/0x14c
>>>> f2fs_set_node_page_dirty+0xd0/0x184
>>>>
>>>> Do not use f2fs_radix_tree_insert() to avoid doing cond_resched() with
>>>> spin_lock() acquired.
>>>>
>>>> Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
>>>> ---
>>>> fs/f2fs/trace.c | 20 +++++++++++++-------
>>>> 1 file changed, 13 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/fs/f2fs/trace.c b/fs/f2fs/trace.c
>>>> index ce2a5eb..d0ab533 100644
>>>> --- a/fs/f2fs/trace.c
>>>> +++ b/fs/f2fs/trace.c
>>>> @@ -14,7 +14,7 @@
>>>> #include "trace.h"
>>>>
>>>> static RADIX_TREE(pids, GFP_ATOMIC);
>>>> -static struct mutex pids_lock;
>>>> +static spinlock_t pids_lock;
>>>> static struct last_io_info last_io;
>>>>
>>>> static inline void __print_last_io(void)
>>>> @@ -58,23 +58,29 @@ void f2fs_trace_pid(struct page *page)
>>>>
>>>> set_page_private(page, (unsigned long)pid);
>>>>
>>>> +retry:
>>>> if (radix_tree_preload(GFP_NOFS))
>>>> return;
>>>>
>>>> - mutex_lock(&pids_lock);
>>>> + spin_lock(&pids_lock);
>>>> p = radix_tree_lookup(&pids, pid);
>>>> if (p == current)
>>>> goto out;
>>>> if (p)
>>>> radix_tree_delete(&pids, pid);
>>>>
>>>> - f2fs_radix_tree_insert(&pids, pid, current);

Do you know why do we have a retry logic here? When anyways we have
called for radix_tree_delete with pid key?
Which should ensure the slot is empty, no?
Then why in the original code (f2fs_radix_tree_insert), we were
retrying. For what condition a retry was needed?

Regards
Ritesh


>>>> + if (radix_tree_insert(&pids, pid, current)) {
>>>> + spin_unlock(&pids_lock);
>>>> + radix_tree_preload_end();
>>>> + cond_resched();
>>>> + goto retry;
>>>> + }
>>>>
>>>> trace_printk("%3x:%3x %4x %-16s\n",
>>>> MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev),
>>>> pid, current->comm);
>>> Hi Sahitya,
>>>
>>> Can trace_printk sleep? For safety, how about moving it out of spinlock?
>>>
>> Hi Chao,
>>
>> Yes, trace_printk() is safe to use in atomic context (unlike printk).
> Hi Sahitya,
>
> Thanks for your confirmation. :)
>
> Reviewed-by: Chao Yu <yuchao0@huawei.com>
>
> Thanks,
>
>> Thanks,
>> Sahitya.
>>
>>> Thanks,
>>>
>>>> out:
>>>> - mutex_unlock(&pids_lock);
>>>> + spin_unlock(&pids_lock);
>>>> radix_tree_preload_end();
>>>> }
>>>>
>>>> @@ -119,7 +125,7 @@ void f2fs_trace_ios(struct f2fs_io_info *fio, int flush)
>>>>
>>>> void f2fs_build_trace_ios(void)
>>>> {
>>>> - mutex_init(&pids_lock);
>>>> + spin_lock_init(&pids_lock);
>>>> }
>>>>
>>>> #define PIDVEC_SIZE 128
>>>> @@ -147,7 +153,7 @@ void f2fs_destroy_trace_ios(void)
>>>> pid_t next_pid = 0;
>>>> unsigned int found;
>>>>
>>>> - mutex_lock(&pids_lock);
>>>> + spin_lock(&pids_lock);
>>>> while ((found = gang_lookup_pids(pid, next_pid, PIDVEC_SIZE))) {
>>>> unsigned idx;
>>>>
>>>> @@ -155,5 +161,5 @@ void f2fs_destroy_trace_ios(void)
>>>> for (idx = 0; idx < found; idx++)
>>>> radix_tree_delete(&pids, pid[idx]);
>>>> }
>>>> - mutex_unlock(&pids_lock);
>>>> + spin_unlock(&pids_lock);
>>>> }
>>>>
>
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> Linux-f2fs-devel@lists.sourceforge.net
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