Messages in this thread | | | Date | Fri, 24 Mar 2023 09:55:42 -0700 | From | Jaegeuk Kim <> | Subject | Re: f2fs: factor out discard_cmd usage from general rb_tree use |
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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 <jaegeuk@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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