On 2019/2/15 12:28, Ritesh Harjani wrote: > > 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 <stumm...@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?
Hi, f2fs_radix_tree_insert is used in many places, it was introduced to used in some paths we should not failed. And here, I guess we used it for the same purpose, if we failed to insert @current pointer into radix, next time, we may not skip calling trace_printk, actually it will print the same current->comm info as previous one, it's redundant. Thanks, > > 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 <yuch...@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); >>>>> } >>>>> >> >> _______________________________________________ >> Linux-f2fs-devel mailing list >> linux-f2fs-de...@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel > > . >