linux-kernel - Re: [PATCH 2/2] block: hold queue lock while iterating in diskstats

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Message-ID: <20220120140126.ntzvrcmczd7pph75@carbon.lan>
Date:   Thu, 20 Jan 2022 15:01:26 +0100
From:   Daniel Wagner <dwagner@...e.de>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH 2/2] block: hold queue lock while iterating in
 diskstats_show

On Thu, Jan 20, 2022 at 09:51:18PM +0800, Ming Lei wrote:
> Then Can you figure out where blk_mq_queue_tag_busy_iter+0x1e4 points to
> in source code? And what is NULL pointer?

Here we go:

/usr/src/debug/kernel-default-5.3.18-59.27.1.x86_64/linux-5.3/linux-obj/../include/linux/sbitmap.h: 249
0xffffffffb244a254 <blk_mq_queue_tag_busy_iter+484>:    mov    (%rax),%rdx

234static inline void __sbitmap_for_each_set(struct sbitmap *sb,
235                                          unsigned int start,
236                                          sb_for_each_fn fn, void *data)
237{
238        unsigned int index;
239        unsigned int nr;
240        unsigned int scanned = 0;
241
242        if (start >= sb->depth)
243                start = 0;
244        index = SB_NR_TO_INDEX(sb, start);
245        nr = SB_NR_TO_BIT(sb, start);
246
247        while (scanned < sb->depth) {
248                unsigned long word;
249                unsigned int depth = min_t(unsigned int,
250                                           sb->map[index].depth - nr,
251                                           sb->depth - scanned);


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