syzbot reported a KCSAN race between fill_mg_cmtime() and inode_set_ctime_to_ts() on inode->i_ctime_{sec,nsec}. stat/getattr can sample inode timestamps while update paths store new values concurrently, so KCSAN can report benign races on these fields. Annotate the timestamp accessors with READ_ONCE()/WRITE_ONCE(), and use the ctime accessor for the remaining ctime loads. This avoids the KCSAN reports without changing timestamp semantics. Fixes: 4e40eff0b573 ("fs: add infrastructure for multigrain timestamps") Reported-by: syzbot+8b3bd9f8a06658479d4a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=8b3bd9f8a06658479d4a Signed-off-by: Yu Peng --- fs/inode.c | 18 +++++++++--------- fs/stat.c | 2 +- include/linux/fs.h | 20 ++++++++++---------- 3 files changed, 20 insertions(+), 20 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 31c5b9ee3a81..95e981b4e19c 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -2833,8 +2833,8 @@ struct timespec64 inode_set_ctime_to_ts(struct inode *inode, struct timespec64 t { trace_inode_set_ctime_to_ts(inode, &ts); set_normalized_timespec64(&ts, ts.tv_sec, ts.tv_nsec); - inode->i_ctime_sec = ts.tv_sec; - inode->i_ctime_nsec = ts.tv_nsec; + WRITE_ONCE(inode->i_ctime_sec, ts.tv_sec); + WRITE_ONCE(inode->i_ctime_nsec, ts.tv_nsec); return ts; } EXPORT_SYMBOL(inode_set_ctime_to_ts); @@ -2908,7 +2908,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode) */ cns = smp_load_acquire(&inode->i_ctime_nsec); if (cns & I_CTIME_QUERIED) { - struct timespec64 ctime = { .tv_sec = inode->i_ctime_sec, + struct timespec64 ctime = { .tv_sec = inode_get_ctime_sec(inode), .tv_nsec = cns & ~I_CTIME_QUERIED }; if (timespec64_compare(&now, &ctime) <= 0) { @@ -2920,7 +2920,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode) mgtime_counter_inc(mg_ctime_updates); /* No need to cmpxchg if it's exactly the same */ - if (cns == now.tv_nsec && inode->i_ctime_sec == now.tv_sec) { + if (cns == now.tv_nsec && inode_get_ctime_sec(inode) == now.tv_sec) { trace_ctime_xchg_skip(inode, &now); goto out; } @@ -2929,7 +2929,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode) /* Try to swap the nsec value into place. */ if (try_cmpxchg(&inode->i_ctime_nsec, &cur, now.tv_nsec)) { /* If swap occurred, then we're (mostly) done */ - inode->i_ctime_sec = now.tv_sec; + WRITE_ONCE(inode->i_ctime_sec, now.tv_sec); trace_ctime_ns_xchg(inode, cns, now.tv_nsec, cur); mgtime_counter_inc(mg_ctime_swaps); } else { @@ -2944,7 +2944,7 @@ struct timespec64 inode_set_ctime_current(struct inode *inode) goto retry; } /* Otherwise, keep the existing ctime */ - now.tv_sec = inode->i_ctime_sec; + now.tv_sec = inode_get_ctime_sec(inode); now.tv_nsec = cur & ~I_CTIME_QUERIED; } out: @@ -2977,7 +2977,7 @@ struct timespec64 inode_set_ctime_deleg(struct inode *inode, struct timespec64 u /* pairs with try_cmpxchg below */ cur = smp_load_acquire(&inode->i_ctime_nsec); cur_ts.tv_nsec = cur & ~I_CTIME_QUERIED; - cur_ts.tv_sec = inode->i_ctime_sec; + cur_ts.tv_sec = inode_get_ctime_sec(inode); /* If the update is older than the existing value, skip it. */ if (timespec64_compare(&update, &cur_ts) <= 0) @@ -3003,7 +3003,7 @@ struct timespec64 inode_set_ctime_deleg(struct inode *inode, struct timespec64 u retry: old = cur; if (try_cmpxchg(&inode->i_ctime_nsec, &cur, update.tv_nsec)) { - inode->i_ctime_sec = update.tv_sec; + WRITE_ONCE(inode->i_ctime_sec, update.tv_sec); mgtime_counter_inc(mg_ctime_swaps); return update; } @@ -3019,7 +3019,7 @@ struct timespec64 inode_set_ctime_deleg(struct inode *inode, struct timespec64 u goto retry; /* Otherwise, it was a new timestamp. */ - cur_ts.tv_sec = inode->i_ctime_sec; + cur_ts.tv_sec = inode_get_ctime_sec(inode); cur_ts.tv_nsec = cur & ~I_CTIME_QUERIED; return cur_ts; } diff --git a/fs/stat.c b/fs/stat.c index 89909746bed1..c461c3054234 100644 --- a/fs/stat.c +++ b/fs/stat.c @@ -53,7 +53,7 @@ void fill_mg_cmtime(struct kstat *stat, u32 request_mask, struct inode *inode) } stat->mtime = inode_get_mtime(inode); - stat->ctime.tv_sec = inode->i_ctime_sec; + stat->ctime.tv_sec = inode_get_ctime_sec(inode); stat->ctime.tv_nsec = (u32)atomic_read(pcn); if (!(stat->ctime.tv_nsec & I_CTIME_QUERIED)) stat->ctime.tv_nsec = ((u32)atomic_fetch_or(I_CTIME_QUERIED, pcn)); diff --git a/include/linux/fs.h b/include/linux/fs.h index d10897b3a1e3..e5b97e324db1 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1598,12 +1598,12 @@ struct timespec64 inode_set_ctime_deleg(struct inode *inode, static inline time64_t inode_get_atime_sec(const struct inode *inode) { - return inode->i_atime_sec; + return READ_ONCE(inode->i_atime_sec); } static inline long inode_get_atime_nsec(const struct inode *inode) { - return inode->i_atime_nsec; + return READ_ONCE(inode->i_atime_nsec); } static inline struct timespec64 inode_get_atime(const struct inode *inode) @@ -1617,8 +1617,8 @@ static inline struct timespec64 inode_get_atime(const struct inode *inode) static inline struct timespec64 inode_set_atime_to_ts(struct inode *inode, struct timespec64 ts) { - inode->i_atime_sec = ts.tv_sec; - inode->i_atime_nsec = ts.tv_nsec; + WRITE_ONCE(inode->i_atime_sec, ts.tv_sec); + WRITE_ONCE(inode->i_atime_nsec, ts.tv_nsec); return ts; } @@ -1633,12 +1633,12 @@ static inline struct timespec64 inode_set_atime(struct inode *inode, static inline time64_t inode_get_mtime_sec(const struct inode *inode) { - return inode->i_mtime_sec; + return READ_ONCE(inode->i_mtime_sec); } static inline long inode_get_mtime_nsec(const struct inode *inode) { - return inode->i_mtime_nsec; + return READ_ONCE(inode->i_mtime_nsec); } static inline struct timespec64 inode_get_mtime(const struct inode *inode) @@ -1651,8 +1651,8 @@ static inline struct timespec64 inode_get_mtime(const struct inode *inode) static inline struct timespec64 inode_set_mtime_to_ts(struct inode *inode, struct timespec64 ts) { - inode->i_mtime_sec = ts.tv_sec; - inode->i_mtime_nsec = ts.tv_nsec; + WRITE_ONCE(inode->i_mtime_sec, ts.tv_sec); + WRITE_ONCE(inode->i_mtime_nsec, ts.tv_nsec); return ts; } @@ -1677,12 +1677,12 @@ static inline struct timespec64 inode_set_mtime(struct inode *inode, static inline time64_t inode_get_ctime_sec(const struct inode *inode) { - return inode->i_ctime_sec; + return READ_ONCE(inode->i_ctime_sec); } static inline long inode_get_ctime_nsec(const struct inode *inode) { - return inode->i_ctime_nsec & ~I_CTIME_QUERIED; + return READ_ONCE(inode->i_ctime_nsec) & ~I_CTIME_QUERIED; } static inline struct timespec64 inode_get_ctime(const struct inode *inode) -- 2.43.0