On Thu, 1 Nov 2018, Steve French wrote:
> The code looks correct. Checking the called function
> iov_iter_get_pages_alloc- it does return negative values despite the
> return type being size_t (and does it intentionally, see code snipped
> below) - presumably we should ignore this warning. See lib/iov_iter.c
> (also the same kind of check is done in fs/splice.c and the other
> callers).
>
> ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
> struct page ***pages, size_t maxsize,
> size_t *start)
The return type is ssize_t not size_t. Putting a negative value into a
size_t variable makes it positive, eg:
#include <stdio.h>
int main () {
size_t x = -1;
printf("%s\n", x < 0 ? "true" : "false");
}
This prints false.
julia
> {
> struct page **p;
>
> if (maxsize > i->count)
> maxsize = i->count;
>
> if (unlikely(i->type & ITER_PIPE))
> return pipe_get_pages_alloc(i, pages, maxsize, start);
> iterate_all_kinds(i, maxsize, v, ({
> unsigned long addr = (unsigned long)v.iov_base;
> size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
> int n;
> int res;
>
> addr &= ~(PAGE_SIZE - 1);
> n = DIV_ROUND_UP(len, PAGE_SIZE);
> p = get_pages_array(n);
> if (!p)
> return -ENOMEM;
> res = get_user_pages_fast(addr, n, (i->type & WRITE)
> != WRITE, p);
> if (unlikely(res < 0)) {
> kvfree(p);
> return res;
> }
> *pages = p;
> return (res == n ? len : res * PAGE_SIZE) - *start;
> 0;}),({
> /* can't be more than PAGE_SIZE */
> *start = v.bv_offset;
> *pages = p = get_pages_array(1);
> if (!p)
> return -ENOMEM;
> get_page(*p = v.bv_page);
> return v.bv_len;
> }),({
> return -EFAULT;
> })
> On Thu, Nov 1, 2018 at 6:24 AM Julia Lawall <julia.lawall@xxxxxxx> wrote:
> >
> > Cur_len can't be less than 0 because it has type size_t, which is
> > unsigned.
> >
> > julia
> >
> > ---------- Forwarded message ----------
> > Date: Thu, 1 Nov 2018 11:37:21 +0800
> > From: kbuild test robot <lkp@xxxxxxxxx>
> > To: kbuild@xxxxxx
> > Cc: Julia Lawall <julia.lawall@xxxxxxx>
> > Subject: [cifs:for-next 7/9] fs/cifs/file.c:3203:7-14: WARNING: Unsigned
> > expression compared with zero: cur_len < 0
> >
> > CC: kbuild-all@xxxxxx
> > CC: linux-cifs@xxxxxxxxxxxxxxx
> > CC: samba-technical@xxxxxxxxxxxxxxx
> > TO: Long Li <longli@xxxxxxxxxxxxx>
> > CC: Steve French <stfrench@xxxxxxxxxxxxx>
> >
> > tree: git://git.samba.org/sfrench/cifs-2.6.git for-next
> > head: 7d8ceb129086fc6c0537fa37d6a4b65f490da006
> > commit: 27d00133fadd8753e1856889dea2da4cb22910a3 [7/9] CIFS: Add support for direct I/O read
> > :::::: branch date:
> > :::::: commit date: 3 hours ago
> >
> > >> fs/cifs/file.c:3203:7-14: WARNING: Unsigned expression compared with zero: cur_len < 0
> >
> > git remote add cifs git://git.samba.org/sfrench/cifs-2.6.git
> > git remote update cifs
> > git checkout 27d00133fadd8753e1856889dea2da4cb22910a3
> > vim +3203 fs/cifs/file.c
> >
> > 27d00133 Long Li 2018-10-31 3164
> > d70b9104 Pavel Shilovsky 2016-11-17 3165 static int
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3166 cifs_send_async_read(loff_t offset, size_t len, struct cifsFileInfo *open_file,
> > 6685c5e2 Pavel Shilovsky 2017-04-25 3167 struct cifs_sb_info *cifs_sb, struct list_head *rdata_list,
> > 6685c5e2 Pavel Shilovsky 2017-04-25 3168 struct cifs_aio_ctx *ctx)
> > ^1da177e Linus Torvalds 2005-04-16 3169 {
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3170 struct cifs_readdata *rdata;
> > bed9da02 Pavel Shilovsky 2014-06-25 3171 unsigned int npages, rsize, credits;
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3172 size_t cur_len;
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3173 int rc;
> > 1c892549 Jeff Layton 2012-05-16 3174 pid_t pid;
> > 25f40259 Pavel Shilovsky 2014-06-25 3175 struct TCP_Server_Info *server;
> > 27d00133 Long Li 2018-10-31 3176 struct page **pagevec;
> > 27d00133 Long Li 2018-10-31 3177 size_t start;
> > 27d00133 Long Li 2018-10-31 3178 struct iov_iter direct_iov = ctx->iter;
> > a70307ee Pavel Shilovsky 2010-12-14 3179
> > 25f40259 Pavel Shilovsky 2014-06-25 3180 server = tlink_tcon(open_file->tlink)->ses->server;
> > fc9c5966 Pavel Shilovsky 2012-09-18 3181
> > d4ffff1f Pavel Shilovsky 2011-05-26 3182 if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_RWPIDFORWARD)
> > d4ffff1f Pavel Shilovsky 2011-05-26 3183 pid = open_file->pid;
> > d4ffff1f Pavel Shilovsky 2011-05-26 3184 else
> > d4ffff1f Pavel Shilovsky 2011-05-26 3185 pid = current->tgid;
> > d4ffff1f Pavel Shilovsky 2011-05-26 3186
> > 27d00133 Long Li 2018-10-31 3187 if (ctx->direct_io)
> > 27d00133 Long Li 2018-10-31 3188 iov_iter_advance(&direct_iov, offset - ctx->pos);
> > 27d00133 Long Li 2018-10-31 3189
> > 1c892549 Jeff Layton 2012-05-16 3190 do {
> > bed9da02 Pavel Shilovsky 2014-06-25 3191 rc = server->ops->wait_mtu_credits(server, cifs_sb->rsize,
> > bed9da02 Pavel Shilovsky 2014-06-25 3192 &rsize, &credits);
> > bed9da02 Pavel Shilovsky 2014-06-25 3193 if (rc)
> > bed9da02 Pavel Shilovsky 2014-06-25 3194 break;
> > bed9da02 Pavel Shilovsky 2014-06-25 3195
> > bed9da02 Pavel Shilovsky 2014-06-25 3196 cur_len = min_t(const size_t, len, rsize);
> > a70307ee Pavel Shilovsky 2010-12-14 3197
> > 27d00133 Long Li 2018-10-31 3198 if (ctx->direct_io) {
> > 27d00133 Long Li 2018-10-31 3199
> > 27d00133 Long Li 2018-10-31 3200 cur_len = iov_iter_get_pages_alloc(
> > 27d00133 Long Li 2018-10-31 3201 &direct_iov, &pagevec,
> > 27d00133 Long Li 2018-10-31 3202 cur_len, &start);
> > 27d00133 Long Li 2018-10-31 @3203 if (cur_len < 0) {
> > 27d00133 Long Li 2018-10-31 3204 cifs_dbg(VFS,
> > 27d00133 Long Li 2018-10-31 3205 "couldn't get user pages (cur_len=%zd)"
> > 27d00133 Long Li 2018-10-31 3206 " iter type %d"
> > 27d00133 Long Li 2018-10-31 3207 " iov_offset %zd count %zd\n",
> > 27d00133 Long Li 2018-10-31 3208 cur_len, direct_iov.type, direct_iov.iov_offset,
> > 27d00133 Long Li 2018-10-31 3209 direct_iov.count);
> > 27d00133 Long Li 2018-10-31 3210 dump_stack();
> > 27d00133 Long Li 2018-10-31 3211 break;
> > 27d00133 Long Li 2018-10-31 3212 }
> > 27d00133 Long Li 2018-10-31 3213 iov_iter_advance(&direct_iov, cur_len);
> > 27d00133 Long Li 2018-10-31 3214
> > 27d00133 Long Li 2018-10-31 3215 rdata = cifs_readdata_direct_alloc(
> > 27d00133 Long Li 2018-10-31 3216 pagevec, cifs_uncached_readv_complete);
> > 27d00133 Long Li 2018-10-31 3217 if (!rdata) {
> > 27d00133 Long Li 2018-10-31 3218 add_credits_and_wake_if(server, credits, 0);
> > 27d00133 Long Li 2018-10-31 3219 rc = -ENOMEM;
> > 27d00133 Long Li 2018-10-31 3220 break;
> > 27d00133 Long Li 2018-10-31 3221 }
> > 27d00133 Long Li 2018-10-31 3222
> > 27d00133 Long Li 2018-10-31 3223 npages = (cur_len + start + PAGE_SIZE-1) / PAGE_SIZE;
> > 27d00133 Long Li 2018-10-31 3224 rdata->page_offset = start;
> > 27d00133 Long Li 2018-10-31 3225 rdata->tailsz = npages > 1 ?
> > 27d00133 Long Li 2018-10-31 3226 cur_len-(PAGE_SIZE-start)-(npages-2)*PAGE_SIZE :
> > 27d00133 Long Li 2018-10-31 3227 cur_len;
> > 27d00133 Long Li 2018-10-31 3228
> > 27d00133 Long Li 2018-10-31 3229 } else {
> > 27d00133 Long Li 2018-10-31 3230
> > 27d00133 Long Li 2018-10-31 3231 npages = DIV_ROUND_UP(cur_len, PAGE_SIZE);
> > 1c892549 Jeff Layton 2012-05-16 3232 /* allocate a readdata struct */
> > 1c892549 Jeff Layton 2012-05-16 3233 rdata = cifs_readdata_alloc(npages,
> > 1c892549 Jeff Layton 2012-05-16 3234 cifs_uncached_readv_complete);
> > 1c892549 Jeff Layton 2012-05-16 3235 if (!rdata) {
> > bed9da02 Pavel Shilovsky 2014-06-25 3236 add_credits_and_wake_if(server, credits, 0);
> > 1c892549 Jeff Layton 2012-05-16 3237 rc = -ENOMEM;
> > bae9f746 Jeff Layton 2014-04-15 3238 break;
> > ^1da177e Linus Torvalds 2005-04-16 3239 }
> > 1c892549 Jeff Layton 2012-05-16 3240
> > c5fab6f4 Jeff Layton 2012-09-19 3241 rc = cifs_read_allocate_pages(rdata, npages);
> > 1c892549 Jeff Layton 2012-05-16 3242 if (rc)
> > 1c892549 Jeff Layton 2012-05-16 3243 goto error;
> > 1c892549 Jeff Layton 2012-05-16 3244
> > 27d00133 Long Li 2018-10-31 3245 rdata->tailsz = PAGE_SIZE;
> > 27d00133 Long Li 2018-10-31 3246 }
> > 27d00133 Long Li 2018-10-31 3247
> > 1c892549 Jeff Layton 2012-05-16 3248 rdata->cfile = cifsFileInfo_get(open_file);
> > c5fab6f4 Jeff Layton 2012-09-19 3249 rdata->nr_pages = npages;
> > 1c892549 Jeff Layton 2012-05-16 3250 rdata->offset = offset;
> > 1c892549 Jeff Layton 2012-05-16 3251 rdata->bytes = cur_len;
> > 1c892549 Jeff Layton 2012-05-16 3252 rdata->pid = pid;
> > 8321fec4 Jeff Layton 2012-09-19 3253 rdata->pagesz = PAGE_SIZE;
> > 8321fec4 Jeff Layton 2012-09-19 3254 rdata->read_into_pages = cifs_uncached_read_into_pages;
> > d70b9104 Pavel Shilovsky 2016-11-17 3255 rdata->copy_into_pages = cifs_uncached_copy_into_pages;
> > bed9da02 Pavel Shilovsky 2014-06-25 3256 rdata->credits = credits;
> > 6685c5e2 Pavel Shilovsky 2017-04-25 3257 rdata->ctx = ctx;
> > 6685c5e2 Pavel Shilovsky 2017-04-25 3258 kref_get(&ctx->refcount);
> > 1c892549 Jeff Layton 2012-05-16 3259
> > 25f40259 Pavel Shilovsky 2014-06-25 3260 if (!rdata->cfile->invalidHandle ||
> > 1fa839b4 Germano Percossi 2017-04-07 3261 !(rc = cifs_reopen_file(rdata->cfile, true)))
> > 25f40259 Pavel Shilovsky 2014-06-25 3262 rc = server->ops->async_readv(rdata);
> > 1c892549 Jeff Layton 2012-05-16 3263 error:
> > 1c892549 Jeff Layton 2012-05-16 3264 if (rc) {
> > bed9da02 Pavel Shilovsky 2014-06-25 3265 add_credits_and_wake_if(server, rdata->credits, 0);
> > 1c892549 Jeff Layton 2012-05-16 3266 kref_put(&rdata->refcount,
> > 1c892549 Jeff Layton 2012-05-16 3267 cifs_uncached_readdata_release);
> > 27d00133 Long Li 2018-10-31 3268 if (rc == -EAGAIN) {
> > 27d00133 Long Li 2018-10-31 3269 iov_iter_revert(&direct_iov, cur_len);
> > 25f40259 Pavel Shilovsky 2014-06-25 3270 continue;
> > 27d00133 Long Li 2018-10-31 3271 }
> > ^1da177e Linus Torvalds 2005-04-16 3272 break;
> > ^1da177e Linus Torvalds 2005-04-16 3273 }
> > 1c892549 Jeff Layton 2012-05-16 3274
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3275 list_add_tail(&rdata->list, rdata_list);
> > 1c892549 Jeff Layton 2012-05-16 3276 offset += cur_len;
> > 1c892549 Jeff Layton 2012-05-16 3277 len -= cur_len;
> > 1c892549 Jeff Layton 2012-05-16 3278 } while (len > 0);
> > 1c892549 Jeff Layton 2012-05-16 3279
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3280 return rc;
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3281 }
> > 0ada36b2 Pavel Shilovsky 2014-06-25 3282
> >
> > ---
> > 0-DAY kernel test infrastructure Open Source Technology Center
> > https://lists.01.org/pipermail/kbuild-all Intel Corporation
>
>
>
> --
> Thanks,
>
> Steve
>
