[newlib-cygwin] Cygwin: lockf: Make lockf() return ENOLCK when too many locks
Takashi Yano
tyan0@sourceware.org
Thu Oct 31 08:43:42 GMT 2024
https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=ae181b0ff1226cf38be8a7f03ff19bf869c87f54
commit ae181b0ff1226cf38be8a7f03ff19bf869c87f54
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date: Sun Oct 20 01:54:00 2024 +0900
Cygwin: lockf: Make lockf() return ENOLCK when too many locks
Previously, lockf() printed a warning message when the number of locks
per file exceeds the limit (MAX_LOCKF_CNT). This patch makes lockf()
return ENOLCK in that case rather than printing the warning message.
Addresses: https://cygwin.com/pipermail/cygwin/2024-October/256528.html
Fixes: 31390e4ca643 ("(inode_t::get_all_locks_list): Use pre-allocated buffer in i_all_lf instead of allocating every lock. Return pointer to start of linked list of locks.")
Reported-by: Christian Franke <Christian.Franke@t-online.de>
Reviewed-by: Corinna Vinschen <corinna@vinschen.de>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
Diff:
---
winsup/cygwin/flock.cc | 82 ++++++++++++++++++++++++++++++++++++++++-----
winsup/cygwin/release/3.5.5 | 4 +++
2 files changed, 78 insertions(+), 8 deletions(-)
diff --git a/winsup/cygwin/flock.cc b/winsup/cygwin/flock.cc
index 5550b3a5b..3821bddd6 100644
--- a/winsup/cygwin/flock.cc
+++ b/winsup/cygwin/flock.cc
@@ -297,6 +297,7 @@ class inode_t
HANDLE i_dir;
HANDLE i_mtx;
uint32_t i_cnt; /* # of threads referencing this instance. */
+ uint32_t i_lock_cnt; /* # of locks for this file */
public:
inode_t (dev_t dev, ino_t ino);
@@ -321,6 +322,8 @@ class inode_t
void unlock_and_remove_if_unused ();
lockf_t *get_all_locks_list ();
+ uint32_t get_lock_count () /* needs get_all_locks_list() */
+ { return i_lock_cnt; }
bool del_my_locks (long long id, HANDLE fhdl);
};
@@ -503,7 +506,8 @@ inode_t::get (dev_t dev, ino_t ino, bool create_if_missing, bool lock)
}
inode_t::inode_t (dev_t dev, ino_t ino)
-: i_lockf (NULL), i_all_lf (NULL), i_dev (dev), i_ino (ino), i_cnt (0L)
+: i_lockf (NULL), i_all_lf (NULL), i_dev (dev), i_ino (ino), i_cnt (0L),
+ i_lock_cnt (0)
{
HANDLE parent_dir;
WCHAR name[48];
@@ -610,17 +614,16 @@ inode_t::get_all_locks_list ()
dbi->ObjectName.Buffer[LOCK_OBJ_NAME_LEN] = L'\0';
if (!newlock.from_obj_name (this, &i_all_lf, dbi->ObjectName.Buffer))
continue;
- if (lock - i_all_lf >= MAX_LOCKF_CNT)
- {
- system_printf ("Warning, can't handle more than %d locks per file.",
- MAX_LOCKF_CNT);
- break;
- }
+ /* This should not be happen. The number of locks is limitted
+ in lf_setlock() and lf_clearlock() so that it does not
+ exceed MAX_LOCKF_CNT. */
+ assert (lock - i_all_lf < MAX_LOCKF_CNT);
if (lock > i_all_lf)
lock[-1].lf_next = lock;
new (lock++) lockf_t (newlock);
}
}
+ i_lock_cnt = lock - i_all_lf;
/* If no lock has been found, return NULL. */
if (lock == i_all_lf)
return NULL;
@@ -1190,6 +1193,12 @@ restart: /* Entry point after a restartable signal came in. */
return -1;
}
+/* The total number of locks shall not exceed MAX_LOCKF_CNT.
+ If once it exceeds, lf_fildoverlap() cannot work correctly.
+ Therefore, lf_setlock() and lf_clearlock() control the
+ total number of locks not to exceed MAX_LOCKF_CNT. When
+ they detect that the operation will cause excess, they
+ return ENOCLK. */
/*
* Set a byte-range lock.
*/
@@ -1346,14 +1355,31 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
*
* Handle any locks that overlap.
*/
+ node->get_all_locks_list (); /* Update lock count */
+ uint32_t lock_cnt = node->get_lock_count ();
+ /* lf_clearlock() sometimes increases the number of locks. Without
+ this room, the unlocking will never succeed in some situation. */
+ const uint32_t room_for_clearlock = 2;
+ const int incr[] = {1, 1, 2, 2, 3, 2};
+ int decr = 0;
+
prev = head;
block = *head;
needtolink = 1;
for (;;)
{
ovcase = lf_findoverlap (block, lock, SELF, &prev, &overlap);
+ /* Estimate the maximum increase in number of the locks that
+ can occur here. If this possibly exceeds the MAX_LOCKF_CNT,
+ return ENOLCK. */
if (ovcase)
- block = overlap->lf_next;
+ {
+ block = overlap->lf_next;
+ HANDLE ov_obj = overlap->lf_obj;
+ decr = (ov_obj && get_obj_handle_count (ov_obj) == 1) ? 1 : 0;
+ }
+ if (needtolink)
+ lock_cnt += incr[ovcase] - decr;
/*
* Six cases:
* 0) no overlap
@@ -1368,6 +1394,8 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
case 0: /* no overlap */
if (needtolink)
{
+ if (lock_cnt > MAX_LOCKF_CNT - room_for_clearlock)
+ return ENOLCK;
*prev = lock;
lock->lf_next = overlap;
lock->create_lock_obj ();
@@ -1380,6 +1408,8 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
* able to acquire it.
* Cygwin: Always wake lock.
*/
+ if (lock_cnt > MAX_LOCKF_CNT - room_for_clearlock)
+ return ENOLCK;
lf_wakelock (overlap, fhdl);
overlap->lf_type = lock->lf_type;
overlap->create_lock_obj ();
@@ -1397,6 +1427,11 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
*clean = lock;
break;
}
+ if (overlap->lf_start < lock->lf_start
+ && overlap->lf_end > lock->lf_end)
+ lock_cnt++;
+ if (lock_cnt > MAX_LOCKF_CNT - room_for_clearlock)
+ return ENOLCK;
if (overlap->lf_start == lock->lf_start)
{
*prev = lock;
@@ -1413,6 +1448,8 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
break;
case 3: /* lock contains overlap */
+ if (needtolink && lock_cnt > MAX_LOCKF_CNT - room_for_clearlock)
+ return ENOLCK;
/*
* If downgrading lock, others may be able to
* acquire it, otherwise take the list.
@@ -1440,6 +1477,8 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
/*
* Add lock after overlap on the list.
*/
+ if (lock_cnt > MAX_LOCKF_CNT - room_for_clearlock)
+ return ENOLCK;
lock->lf_next = overlap->lf_next;
overlap->lf_next = lock;
overlap->lf_end = lock->lf_start - 1;
@@ -1456,6 +1495,8 @@ lf_setlock (lockf_t *lock, inode_t *node, lockf_t **clean, HANDLE fhdl)
*/
if (needtolink)
{
+ if (lock_cnt > MAX_LOCKF_CNT - room_for_clearlock)
+ return ENOLCK;
*prev = lock;
lock->lf_next = overlap;
lock->create_lock_obj ();
@@ -1483,12 +1524,35 @@ lf_clearlock (lockf_t *unlock, lockf_t **clean, HANDLE fhdl)
lockf_t *lf = *head;
lockf_t *overlap, **prev;
int ovcase;
+ inode_t *node = lf->lf_inode;
+ tmp_pathbuf tp;
+ node->i_all_lf = (lockf_t *) tp.w_get ();
+ node->get_all_locks_list (); /* Update lock count */
+ uint32_t lock_cnt = node->get_lock_count ();
+ bool first_loop = true;
if (lf == NOLOCKF)
return 0;
prev = head;
while ((ovcase = lf_findoverlap (lf, unlock, SELF, &prev, &overlap)))
{
+ /* Estimate the maximum increase in number of the locks that
+ can occur here. If this possibly exceeds the MAX_LOCKF_CNT,
+ return ENOLCK. */
+ HANDLE ov_obj = overlap->lf_obj;
+ if (first_loop)
+ {
+ const int incr[] = {0, 0, 1, 1, 2, 1};
+ int decr = (ov_obj && get_obj_handle_count (ov_obj) == 1) ? 1 : 0;
+ lock_cnt += incr[ovcase] - decr;
+ if (ovcase == 2
+ && overlap->lf_start < unlock->lf_start
+ && overlap->lf_end > unlock->lf_end)
+ lock_cnt++;
+ if (lock_cnt > MAX_LOCKF_CNT)
+ return ENOLCK;
+ }
+
/*
* Wakeup the list of locks to be retried.
*/
@@ -1521,6 +1585,7 @@ lf_clearlock (lockf_t *unlock, lockf_t **clean, HANDLE fhdl)
lf = overlap->lf_next;
overlap->lf_next = *clean;
*clean = overlap;
+ first_loop = false;
continue;
case 4: /* overlap starts before lock */
@@ -1528,6 +1593,7 @@ lf_clearlock (lockf_t *unlock, lockf_t **clean, HANDLE fhdl)
prev = &overlap->lf_next;
lf = overlap->lf_next;
overlap->create_lock_obj ();
+ first_loop = false;
continue;
case 5: /* overlap ends after lock */
diff --git a/winsup/cygwin/release/3.5.5 b/winsup/cygwin/release/3.5.5
index ca96edf04..2dba4aa8f 100644
--- a/winsup/cygwin/release/3.5.5
+++ b/winsup/cygwin/release/3.5.5
@@ -16,3 +16,7 @@ Fixes:
- Fix lockf() error which occurs when adding a new lock over multiple
locks.
Addresses: https://cygwin.com/pipermail/cygwin/2024-October/256528.html
+
+- Make lockf() return ENOLCK when the number of locks exceeds
+ MAX_LOCKF_CNT rather than printing a warning message.
+ Addresses: https://cygwin.com/pipermail/cygwin/2024-October/256528.html
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