Commit 7485d0d3758e8e6491a5c9468114e74dc050785d
Committed by
Ingo Molnar
1 parent
7284ce6c9f
Exists in
master
and in
39 other branches
futexes: Remove rw parameter from get_futex_key()
Currently, futexes have two problem: A) The current futex code doesn't handle private file mappings properly. get_futex_key() uses PageAnon() to distinguish file and anon, which can cause the following bad scenario: 1) thread-A call futex(private-mapping, FUTEX_WAIT), it sleeps on file mapping object. 2) thread-B writes a variable and it makes it cow. 3) thread-B calls futex(private-mapping, FUTEX_WAKE), it wakes up blocked thread on the anonymous page. (but it's nothing) B) Current futex code doesn't handle zero page properly. Read mode get_user_pages() can return zero page, but current futex code doesn't handle it at all. Then, zero page makes infinite loop internally. The solution is to use write mode get_user_page() always for page lookup. It prevents the lookup of both file page of private mappings and zero page. Performance concerns: Probaly very little, because glibc always initialize variables for futex before to call futex(). It means glibc users never see the overhead of this patch. Compatibility concerns: This patch has few compatibility issues. After this patch, FUTEX_WAIT require writable access to futex variables (read-only mappings makes EFAULT). But practically it's not a problem, glibc always initalizes variables for futexes explicitly - nobody uses read-only mappings. Reported-by: Hugh Dickins <hugh.dickins@tiscali.co.uk> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Darren Hart <dvhltc@us.ibm.com> Cc: <stable@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Ulrich Drepper <drepper@gmail.com> LKML-Reference: <20100105162633.45A2.A69D9226@jp.fujitsu.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Showing 1 changed file with 12 additions and 15 deletions Side-by-side Diff
kernel/futex.c
... | ... | @@ -203,8 +203,6 @@ |
203 | 203 | * @uaddr: virtual address of the futex |
204 | 204 | * @fshared: 0 for a PROCESS_PRIVATE futex, 1 for PROCESS_SHARED |
205 | 205 | * @key: address where result is stored. |
206 | - * @rw: mapping needs to be read/write (values: VERIFY_READ, | |
207 | - * VERIFY_WRITE) | |
208 | 206 | * |
209 | 207 | * Returns a negative error code or 0 |
210 | 208 | * The key words are stored in *key on success. |
... | ... | @@ -216,7 +214,7 @@ |
216 | 214 | * lock_page() might sleep, the caller should not hold a spinlock. |
217 | 215 | */ |
218 | 216 | static int |
219 | -get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw) | |
217 | +get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key) | |
220 | 218 | { |
221 | 219 | unsigned long address = (unsigned long)uaddr; |
222 | 220 | struct mm_struct *mm = current->mm; |
... | ... | @@ -239,7 +237,7 @@ |
239 | 237 | * but access_ok() should be faster than find_vma() |
240 | 238 | */ |
241 | 239 | if (!fshared) { |
242 | - if (unlikely(!access_ok(rw, uaddr, sizeof(u32)))) | |
240 | + if (unlikely(!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))) | |
243 | 241 | return -EFAULT; |
244 | 242 | key->private.mm = mm; |
245 | 243 | key->private.address = address; |
... | ... | @@ -248,7 +246,7 @@ |
248 | 246 | } |
249 | 247 | |
250 | 248 | again: |
251 | - err = get_user_pages_fast(address, 1, rw == VERIFY_WRITE, &page); | |
249 | + err = get_user_pages_fast(address, 1, 1, &page); | |
252 | 250 | if (err < 0) |
253 | 251 | return err; |
254 | 252 | |
... | ... | @@ -867,7 +865,7 @@ |
867 | 865 | if (!bitset) |
868 | 866 | return -EINVAL; |
869 | 867 | |
870 | - ret = get_futex_key(uaddr, fshared, &key, VERIFY_READ); | |
868 | + ret = get_futex_key(uaddr, fshared, &key); | |
871 | 869 | if (unlikely(ret != 0)) |
872 | 870 | goto out; |
873 | 871 | |
874 | 872 | |
... | ... | @@ -913,10 +911,10 @@ |
913 | 911 | int ret, op_ret; |
914 | 912 | |
915 | 913 | retry: |
916 | - ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ); | |
914 | + ret = get_futex_key(uaddr1, fshared, &key1); | |
917 | 915 | if (unlikely(ret != 0)) |
918 | 916 | goto out; |
919 | - ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE); | |
917 | + ret = get_futex_key(uaddr2, fshared, &key2); | |
920 | 918 | if (unlikely(ret != 0)) |
921 | 919 | goto out_put_key1; |
922 | 920 | |
923 | 921 | |
... | ... | @@ -1175,11 +1173,10 @@ |
1175 | 1173 | pi_state = NULL; |
1176 | 1174 | } |
1177 | 1175 | |
1178 | - ret = get_futex_key(uaddr1, fshared, &key1, VERIFY_READ); | |
1176 | + ret = get_futex_key(uaddr1, fshared, &key1); | |
1179 | 1177 | if (unlikely(ret != 0)) |
1180 | 1178 | goto out; |
1181 | - ret = get_futex_key(uaddr2, fshared, &key2, | |
1182 | - requeue_pi ? VERIFY_WRITE : VERIFY_READ); | |
1179 | + ret = get_futex_key(uaddr2, fshared, &key2); | |
1183 | 1180 | if (unlikely(ret != 0)) |
1184 | 1181 | goto out_put_key1; |
1185 | 1182 | |
... | ... | @@ -1738,7 +1735,7 @@ |
1738 | 1735 | */ |
1739 | 1736 | retry: |
1740 | 1737 | q->key = FUTEX_KEY_INIT; |
1741 | - ret = get_futex_key(uaddr, fshared, &q->key, VERIFY_READ); | |
1738 | + ret = get_futex_key(uaddr, fshared, &q->key); | |
1742 | 1739 | if (unlikely(ret != 0)) |
1743 | 1740 | return ret; |
1744 | 1741 | |
... | ... | @@ -1904,7 +1901,7 @@ |
1904 | 1901 | q.requeue_pi_key = NULL; |
1905 | 1902 | retry: |
1906 | 1903 | q.key = FUTEX_KEY_INIT; |
1907 | - ret = get_futex_key(uaddr, fshared, &q.key, VERIFY_WRITE); | |
1904 | + ret = get_futex_key(uaddr, fshared, &q.key); | |
1908 | 1905 | if (unlikely(ret != 0)) |
1909 | 1906 | goto out; |
1910 | 1907 | |
... | ... | @@ -2023,7 +2020,7 @@ |
2023 | 2020 | if ((uval & FUTEX_TID_MASK) != task_pid_vnr(current)) |
2024 | 2021 | return -EPERM; |
2025 | 2022 | |
2026 | - ret = get_futex_key(uaddr, fshared, &key, VERIFY_WRITE); | |
2023 | + ret = get_futex_key(uaddr, fshared, &key); | |
2027 | 2024 | if (unlikely(ret != 0)) |
2028 | 2025 | goto out; |
2029 | 2026 | |
... | ... | @@ -2215,7 +2212,7 @@ |
2215 | 2212 | rt_waiter.task = NULL; |
2216 | 2213 | |
2217 | 2214 | key2 = FUTEX_KEY_INIT; |
2218 | - ret = get_futex_key(uaddr2, fshared, &key2, VERIFY_WRITE); | |
2215 | + ret = get_futex_key(uaddr2, fshared, &key2); | |
2219 | 2216 | if (unlikely(ret != 0)) |
2220 | 2217 | goto out; |
2221 | 2218 |
-
mentioned in commit 316933