On 03/24, Colin King (gmail) wrote:
> Hi,
>
> static analysis with clang scan build has detected a potential issue
> introduced by the following commit:
>
> commit 7e9775a516ff6c1e73ee2b42ec563cafee38f42f
> Author: Jaegeuk Kim <jaeg...@kernel.org>
> Date: Fri Mar 10 11:12:35 2023 -0800
>
> f2fs: factor out discard_cmd usage from general rb_tree use
Good catch!
I found the bug and will post v2 soon.
>
>
> The warning is as follows:
>
> fs/f2fs/segment.c:1425:4: warning: Value stored to 'tdc' is never read
> [deadcode.DeadStores]
>
> The while loop in function __update_discard_tree_range is as follows (+ my
> annotations):
>
>
> while (1) {
> struct rb_node *node;
> struct discard_cmd *tdc = NULL;
>
> ### tdc is set to NULL
>
> if (prev_dc) {
> di.lstart = prev_dc->di.lstart + prev_dc->di.len;
> if (di.lstart < lstart)
> di.lstart = lstart;
> if (di.lstart >= end)
> break;
>
> if (!next_dc || next_dc->di.lstart > end)
> di.len = end - di.lstart;
> else
> di.len = next_dc->di.lstart - di.lstart;
> di.start = start + di.lstart - lstart;
> }
>
> if (!di.len)
> goto next;
>
> if (prev_dc && prev_dc->state == D_PREP &&
> prev_dc->bdev == bdev &&
> __is_discard_back_mergeable(&di, &prev_dc->di,
>
> max_discard_blocks)) {
> prev_dc->di.len += di.len;
> dcc->undiscard_blks += di.len;
> __relocate_discard_cmd(dcc, prev_dc);
> di = prev_dc->di;
> tdc = prev_dc;
>
> ### tdc is set to prev_dc, however, it is not not read any more with th
> introduction of the "goto next"" statement introduced in the commit
> mentioned earlier
>
> goto next;
> }
>
> if (next_dc && next_dc->state == D_PREP &&
> next_dc->bdev == bdev &&
> __is_discard_front_mergeable(&di, &next_dc->di,
>
> max_discard_blocks)) {
> next_dc->di.lstart = di.lstart;
> next_dc->di.len += di.len;
> next_dc->di.start = di.start;
> dcc->undiscard_blks += di.len;
> __relocate_discard_cmd(dcc, next_dc);
>
> ### tdc is always NULL, there is no path to this code where tdc is ever set
> to a non-NULL value.
>
> if (tdc)
> __remove_discard_cmd(sbi, tdc);
> goto next;
> }
>
> __insert_discard_cmd(sbi, bdev, di.lstart, di.start,
> di.len);
> next:
> prev_dc = next_dc;
> if (!prev_dc)
> break;
>
> node = rb_next(&prev_dc->rb_node);
> next_dc = rb_entry_safe(node, struct discard_cmd, rb_node);
> }
>
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