On 7/14/20 6:10 AM, Matthew Wilcox wrote: > On Tue, Jul 14, 2020 at 06:05:09AM -0700, [email protected] wrote: >> From: Tom Rix <[email protected]> >> >> clang static analysis flags this error >> >> inode.c:1083:5: warning: Argument to kfree() is the address of the >> local variable 'unf_single', which is not memory allocated by >> malloc() [unix.Malloc] >> kfree(un); >> ^~~~~~~~~ >> Assignment of 'un' >> >> /* >> * We use this in case we need to allocate >> * only one block which is a fastpath >> */ >> unp_t unf_single = 0; >> >> ... >> >> if (blocks_needed == 1) { >> un = &unf_single; >> } else { >> un = kcalloc(min(blocks_needed, max_to_insert), >> UNFM_P_SIZE, GFP_NOFS); >> if (!un) { >> un = &unf_single; >> blocks_needed = 1; >> max_to_insert = 0; >> } >> } >> >> The logic to free 'un' >> >> if (blocks_needed != 1) >> kfree(un); >> >> Because the kcalloc failure falls back to using unf_single, >> the if-check for the free is wrong. > I think you mean "Because clang's static analysis is limited, it > warns incorrectly about this". There's no path to get to the > kfree with blocks_needed != 1 and un being equal to &unf_single.
Ok. >> So improve the check. >> >> Signed-off-by: Tom Rix <[email protected]> >> --- >> fs/reiserfs/inode.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/reiserfs/inode.c b/fs/reiserfs/inode.c >> index 1509775da040..4d62148e43e6 100644 >> --- a/fs/reiserfs/inode.c >> +++ b/fs/reiserfs/inode.c >> @@ -1079,7 +1079,7 @@ int reiserfs_get_block(struct inode *inode, sector_t >> block, >> UNFM_P_SIZE * >> blocks_needed); >> >> - if (blocks_needed != 1) >> + if (un != &unf_single) >> kfree(un); > I don't actually object to this patch, but your analysis of clang's > analysis is wrong. >
