ср, 30 окт. 2019 г. в 08:46, Pavel Shilovsky <piastryyy@xxxxxxxxx>:
>
> вт, 29 окт. 2019 г. в 19:59, Ronnie Sahlberg <lsahlber@xxxxxxxxxx>:
> >
> > This patch moves the final part of the cifsFileInfo_put() logic where we
> > need a write lock on lock_sem to be processed in a separate thread that
> > holds no other locks.
> > This is to prevent deadlocks like the one below:
> >
> > > there are 6 processes looping to while trying to down_write
> > > cinode->lock_sem, 5 of them from _cifsFileInfo_put, and one from
> > > cifs_new_fileinfo
> > >
> > > and there are 5 other processes which are blocked, several of them
> > > waiting on either PG_writeback or PG_locked (which are both set), all
> > > for the same page of the file
> > >
> > > 2 inode_lock() (inode->i_rwsem) for the file
> > > 1 wait_on_page_writeback() for the page
> > > 1 down_read(inode->i_rwsem) for the inode of the directory
> > > 1 inode_lock()(inode->i_rwsem) for the inode of the directory
> > > 1 __lock_page
> > >
> > >
> > > so processes are blocked waiting on:
> > > page flags PG_locked and PG_writeback for one specific page
> > > inode->i_rwsem for the directory
> > > inode->i_rwsem for the file
> > > cifsInodeInflock_sem
> > >
> > >
> > >
> > > here are the more gory details (let me know if I need to provide
> > > anything more/better):
> > >
> > > [0 00:48:22.765] [UN] PID: 8863 TASK: ffff8c691547c5c0 CPU: 3
> > > COMMAND: "reopen_file"
> > > #0 [ffff9965007e3ba8] __schedule at ffffffff9b6e6095
> > > #1 [ffff9965007e3c38] schedule at ffffffff9b6e64df
> > > #2 [ffff9965007e3c48] rwsem_down_write_slowpath at ffffffff9af283d7
> > > #3 [ffff9965007e3cb8] legitimize_path at ffffffff9b0f975d
> > > #4 [ffff9965007e3d08] path_openat at ffffffff9b0fe55d
> > > #5 [ffff9965007e3dd8] do_filp_open at ffffffff9b100a33
> > > #6 [ffff9965007e3ee0] do_sys_open at ffffffff9b0eb2d6
> > > #7 [ffff9965007e3f38] do_syscall_64 at ffffffff9ae04315
> > > * (I think legitimize_path is bogus)
> > >
> > > in path_openat
> > > } else {
> > > const char *s = path_init(nd, flags);
> > > while (!(error = link_path_walk(s, nd)) &&
> > > (error = do_last(nd, file, op)) > 0) { <<<<
> > >
> > > do_last:
> > > if (open_flag & O_CREAT)
> > > inode_lock(dir->d_inode); <<<<
> > > else
> > > so it's trying to take inode->i_rwsem for the directory
> > >
> > > DENTRY INODE SUPERBLK TYPE PATH
> > > ffff8c68bb8e79c0 ffff8c691158ef20 ffff8c6915bf9000 DIR /mnt/vm1_smb/
> > > inode.i_rwsem is ffff8c691158efc0
> > >
> > > <struct rw_semaphore 0xffff8c691158efc0>:
> > > owner: <struct task_struct 0xffff8c6914275d00> (UN - 8856 -
> > > reopen_file), counter: 0x0000000000000003
> > > waitlist: 2
> > > 0xffff9965007e3c90 8863 reopen_file UN 0 1:29:22.926
> > > RWSEM_WAITING_FOR_WRITE
> > > 0xffff996500393e00 9802 ls UN 0 1:17:26.700
> > > RWSEM_WAITING_FOR_READ
> > >
> > >
> > > the owner of the inode.i_rwsem of the directory is:
> > >
> > > [0 00:00:00.109] [UN] PID: 8856 TASK: ffff8c6914275d00 CPU: 3
> > > COMMAND: "reopen_file"
> > > #0 [ffff99650065b828] __schedule at ffffffff9b6e6095
> > > #1 [ffff99650065b8b8] schedule at ffffffff9b6e64df
> > > #2 [ffff99650065b8c8] schedule_timeout at ffffffff9b6e9f89
> > > #3 [ffff99650065b940] msleep at ffffffff9af573a9
> > > #4 [ffff99650065b948] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> > > #5 [ffff99650065ba38] cifs_writepage_locked at ffffffffc0a0b8f3 [cifs]
> > > #6 [ffff99650065bab0] cifs_launder_page at ffffffffc0a0bb72 [cifs]
> > > #7 [ffff99650065bb30] invalidate_inode_pages2_range at ffffffff9b04d4bd
> > > #8 [ffff99650065bcb8] cifs_invalidate_mapping at ffffffffc0a11339 [cifs]
> > > #9 [ffff99650065bcd0] cifs_revalidate_mapping at ffffffffc0a1139a [cifs]
> > > #10 [ffff99650065bcf0] cifs_d_revalidate at ffffffffc0a014f6 [cifs]
> > > #11 [ffff99650065bd08] path_openat at ffffffff9b0fe7f7
> > > #12 [ffff99650065bdd8] do_filp_open at ffffffff9b100a33
> > > #13 [ffff99650065bee0] do_sys_open at ffffffff9b0eb2d6
> > > #14 [ffff99650065bf38] do_syscall_64 at ffffffff9ae04315
> > >
> > > cifs_launder_page is for page 0xffffd1e2c07d2480
> > >
> > > crash> page.index,mapping,flags 0xffffd1e2c07d2480
> > > index = 0x8
> > > mapping = 0xffff8c68f3cd0db0
> > > flags = 0xfffffc0008095
> > >
> > > PAGE-FLAG BIT VALUE
> > > PG_locked 0 0000001
> > > PG_uptodate 2 0000004
> > > PG_lru 4 0000010
> > > PG_waiters 7 0000080
> > > PG_writeback 15 0008000
> > >
> > >
> > > inode is ffff8c68f3cd0c40
> > > inode.i_rwsem is ffff8c68f3cd0ce0
> > > DENTRY INODE SUPERBLK TYPE PATH
> > > ffff8c68a1f1b480 ffff8c68f3cd0c40 ffff8c6915bf9000 REG
> > > /mnt/vm1_smb/testfile.8853
> > >
> > >
> > > this process holds the inode->i_rwsem for the parent directory, is
> > > laundering a page attached to the inode of the file it's opening, and in
> > > _cifsFileInfo_put is trying to down_write the cifsInodeInflock_sem
> > > for the file itself.
> > >
> > >
> > > <struct rw_semaphore 0xffff8c68f3cd0ce0>:
> > > owner: <struct task_struct 0xffff8c6914272e80> (UN - 8854 -
> > > reopen_file), counter: 0x0000000000000003
> > > waitlist: 1
> > > 0xffff9965005dfd80 8855 reopen_file UN 0 1:29:22.912
> > > RWSEM_WAITING_FOR_WRITE
> > >
> > > this is the inode.i_rwsem for the file
> > >
> > > the owner:
> > >
> > > [0 00:48:22.739] [UN] PID: 8854 TASK: ffff8c6914272e80 CPU: 2
> > > COMMAND: "reopen_file"
> > > #0 [ffff99650054fb38] __schedule at ffffffff9b6e6095
> > > #1 [ffff99650054fbc8] schedule at ffffffff9b6e64df
> > > #2 [ffff99650054fbd8] io_schedule at ffffffff9b6e68e2
> > > #3 [ffff99650054fbe8] __lock_page at ffffffff9b03c56f
> > > #4 [ffff99650054fc80] pagecache_get_page at ffffffff9b03dcdf
> > > #5 [ffff99650054fcc0] grab_cache_page_write_begin at ffffffff9b03ef4c
> > > #6 [ffff99650054fcd0] cifs_write_begin at ffffffffc0a064ec [cifs]
> > > #7 [ffff99650054fd30] generic_perform_write at ffffffff9b03bba4
> > > #8 [ffff99650054fda8] __generic_file_write_iter at ffffffff9b04060a
> > > #9 [ffff99650054fdf0] cifs_strict_writev.cold.70 at ffffffffc0a4469b [cifs]
> > > #10 [ffff99650054fe48] new_sync_write at ffffffff9b0ec1dd
> > > #11 [ffff99650054fed0] vfs_write at ffffffff9b0eed35
> > > #12 [ffff99650054ff00] ksys_write at ffffffff9b0eefd9
> > > #13 [ffff99650054ff38] do_syscall_64 at ffffffff9ae04315
> > >
> > > the process holds the inode->i_rwsem for the file to which it's writing,
> > > and is trying to __lock_page for the same page as in the other processes
> > >
> > >
> > > the other tasks:
> > > [0 00:00:00.028] [UN] PID: 8859 TASK: ffff8c6915479740 CPU: 2
> > > COMMAND: "reopen_file"
> > > #0 [ffff9965007b39d8] __schedule at ffffffff9b6e6095
> > > #1 [ffff9965007b3a68] schedule at ffffffff9b6e64df
> > > #2 [ffff9965007b3a78] schedule_timeout at ffffffff9b6e9f89
> > > #3 [ffff9965007b3af0] msleep at ffffffff9af573a9
> > > #4 [ffff9965007b3af8] cifs_new_fileinfo.cold.61 at ffffffffc0a42a07 [cifs]
> > > #5 [ffff9965007b3b78] cifs_open at ffffffffc0a0709d [cifs]
> > > #6 [ffff9965007b3cd8] do_dentry_open at ffffffff9b0e9b7a
> > > #7 [ffff9965007b3d08] path_openat at ffffffff9b0fe34f
> > > #8 [ffff9965007b3dd8] do_filp_open at ffffffff9b100a33
> > > #9 [ffff9965007b3ee0] do_sys_open at ffffffff9b0eb2d6
> > > #10 [ffff9965007b3f38] do_syscall_64 at ffffffff9ae04315
> > >
> > > this is opening the file, and is trying to down_write cinode->lock_sem
> > >
> > >
> > > [0 00:00:00.041] [UN] PID: 8860 TASK: ffff8c691547ae80 CPU: 2
> > > COMMAND: "reopen_file"
> > > [0 00:00:00.057] [UN] PID: 8861 TASK: ffff8c6915478000 CPU: 3
> > > COMMAND: "reopen_file"
> > > [0 00:00:00.059] [UN] PID: 8858 TASK: ffff8c6914271740 CPU: 2
> > > COMMAND: "reopen_file"
> > > [0 00:00:00.109] [UN] PID: 8862 TASK: ffff8c691547dd00 CPU: 6
> > > COMMAND: "reopen_file"
> > > #0 [ffff9965007c3c78] __schedule at ffffffff9b6e6095
> > > #1 [ffff9965007c3d08] schedule at ffffffff9b6e64df
> > > #2 [ffff9965007c3d18] schedule_timeout at ffffffff9b6e9f89
> > > #3 [ffff9965007c3d90] msleep at ffffffff9af573a9
> > > #4 [ffff9965007c3d98] _cifsFileInfo_put.cold.63 at ffffffffc0a42dd6 [cifs]
> > > #5 [ffff9965007c3e88] cifs_close at ffffffffc0a07aaf [cifs]
> > > #6 [ffff9965007c3ea0] __fput at ffffffff9b0efa6e
> > > #7 [ffff9965007c3ee8] task_work_run at ffffffff9aef1614
> > > #8 [ffff9965007c3f20] exit_to_usermode_loop at ffffffff9ae03d6f
> > > #9 [ffff9965007c3f38] do_syscall_64 at ffffffff9ae0444c
> > >
> > > closing the file, and trying to down_write cifsi->lock_sem
> > >
> > >
> > > [0 00:48:22.839] [UN] PID: 8857 TASK: ffff8c6914270000 CPU: 7
> > > COMMAND: "reopen_file"
> > > #0 [ffff9965006a7cc8] __schedule at ffffffff9b6e6095
> > > #1 [ffff9965006a7d58] schedule at ffffffff9b6e64df
> > > #2 [ffff9965006a7d68] io_schedule at ffffffff9b6e68e2
> > > #3 [ffff9965006a7d78] wait_on_page_bit at ffffffff9b03cac6
> > > #4 [ffff9965006a7e10] __filemap_fdatawait_range at ffffffff9b03b028
> > > #5 [ffff9965006a7ed8] filemap_write_and_wait at ffffffff9b040165
> > > #6 [ffff9965006a7ef0] cifs_flush at ffffffffc0a0c2fa [cifs]
> > > #7 [ffff9965006a7f10] filp_close at ffffffff9b0e93f1
> > > #8 [ffff9965006a7f30] __x64_sys_close at ffffffff9b0e9a0e
> > > #9 [ffff9965006a7f38] do_syscall_64 at ffffffff9ae04315
> > >
> > > in __filemap_fdatawait_range
> > > wait_on_page_writeback(page);
> > > for the same page of the file
> > >
> > >
> > >
> > > [0 00:48:22.718] [UN] PID: 8855 TASK: ffff8c69142745c0 CPU: 7
> > > COMMAND: "reopen_file"
> > > #0 [ffff9965005dfc98] __schedule at ffffffff9b6e6095
> > > #1 [ffff9965005dfd28] schedule at ffffffff9b6e64df
> > > #2 [ffff9965005dfd38] rwsem_down_write_slowpath at ffffffff9af283d7
> > > #3 [ffff9965005dfdf0] cifs_strict_writev at ffffffffc0a0c40a [cifs]
> > > #4 [ffff9965005dfe48] new_sync_write at ffffffff9b0ec1dd
> > > #5 [ffff9965005dfed0] vfs_write at ffffffff9b0eed35
> > > #6 [ffff9965005dff00] ksys_write at ffffffff9b0eefd9
> > > #7 [ffff9965005dff38] do_syscall_64 at ffffffff9ae04315
> > >
> > > inode_lock(inode);
> > >
> > >
> > > and one 'ls' later on, to see whether the rest of the mount is available
> > > (the test file is in the root, so we get blocked up on the directory
> > > ->i_rwsem), so the entire mount is unavailable
> > >
> > > [0 00:36:26.473] [UN] PID: 9802 TASK: ffff8c691436ae80 CPU: 4
> > > COMMAND: "ls"
> > > #0 [ffff996500393d28] __schedule at ffffffff9b6e6095
> > > #1 [ffff996500393db8] schedule at ffffffff9b6e64df
> > > #2 [ffff996500393dc8] rwsem_down_read_slowpath at ffffffff9b6e9421
> > > #3 [ffff996500393e78] down_read_killable at ffffffff9b6e95e2
> > > #4 [ffff996500393e88] iterate_dir at ffffffff9b103c56
> > > #5 [ffff996500393ec8] ksys_getdents64 at ffffffff9b104b0c
> > > #6 [ffff996500393f30] __x64_sys_getdents64 at ffffffff9b104bb6
> > > #7 [ffff996500393f38] do_syscall_64 at ffffffff9ae04315
> > >
> > > in iterate_dir:
> > > if (shared)
> > > res = down_read_killable(&inode->i_rwsem); <<<<
> > > else
> > > res = down_write_killable(&inode->i_rwsem);
> > >
> >
> > Signed-off-by: Ronnie Sahlberg <lsahlber@xxxxxxxxxx>
> > ---
> > fs/cifs/cifsfs.c | 13 +++++++-
> > fs/cifs/cifsglob.h | 3 +-
> > fs/cifs/file.c | 91 ++++++++++++++++++++++++++++++++++--------------------
> > 3 files changed, 72 insertions(+), 35 deletions(-)
> >
> > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > index e4e3b573d20c..f8e201c45ccb 100644
> > --- a/fs/cifs/cifsfs.c
> > +++ b/fs/cifs/cifsfs.c
> > @@ -119,6 +119,7 @@ extern mempool_t *cifs_mid_poolp;
> >
> > struct workqueue_struct *cifsiod_wq;
> > struct workqueue_struct *decrypt_wq;
> > +struct workqueue_struct *fileinfo_put_wq;
> > struct workqueue_struct *cifsoplockd_wq;
> > __u32 cifs_lock_secret;
> >
> > @@ -1557,11 +1558,18 @@ init_cifs(void)
> > goto out_destroy_cifsiod_wq;
> > }
> >
> > + fileinfo_put_wq = alloc_workqueue("cifsfileinfoput",
> > + WQ_UNBOUND|WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> > + if (!fileinfo_put_wq) {
> > + rc = -ENOMEM;
> > + goto out_destroy_decrypt_wq;
> > + }
> > +
> > cifsoplockd_wq = alloc_workqueue("cifsoplockd",
> > WQ_FREEZABLE|WQ_MEM_RECLAIM, 0);
> > if (!cifsoplockd_wq) {
> > rc = -ENOMEM;
> > - goto out_destroy_decrypt_wq;
> > + goto out_destroy_fileinfo_put_wq;
> > }
> >
> > rc = cifs_fscache_register();
> > @@ -1627,6 +1635,8 @@ init_cifs(void)
> > cifs_fscache_unregister();
> > out_destroy_cifsoplockd_wq:
> > destroy_workqueue(cifsoplockd_wq);
> > +out_destroy_fileinfo_put_wq:
> > + destroy_workqueue(fileinfo_put_wq);
> > out_destroy_decrypt_wq:
> > destroy_workqueue(decrypt_wq);
> > out_destroy_cifsiod_wq:
> > @@ -1656,6 +1666,7 @@ exit_cifs(void)
> > cifs_fscache_unregister();
> > destroy_workqueue(cifsoplockd_wq);
> > destroy_workqueue(decrypt_wq);
> > + destroy_workqueue(fileinfo_put_wq);
> > destroy_workqueue(cifsiod_wq);
> > cifs_proc_clean();
> > }
> > diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> > index d78bfcc19156..0819b6498a3c 100644
> > --- a/fs/cifs/cifsglob.h
> > +++ b/fs/cifs/cifsglob.h
> > @@ -1265,6 +1265,7 @@ struct cifsFileInfo {
> > struct mutex fh_mutex; /* prevents reopen race after dead ses*/
> > struct cifs_search_info srch_inf;
> > struct work_struct oplock_break; /* work for oplock breaks */
> > + struct work_struct put; /* work for the final part of _put */
> > };
> >
> > struct cifs_io_parms {
> > @@ -1370,7 +1371,6 @@ cifsFileInfo_get_locked(struct cifsFileInfo *cifs_file)
> > }
> >
> > struct cifsFileInfo *cifsFileInfo_get(struct cifsFileInfo *cifs_file);
> > -void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_hdlr);
> > void cifsFileInfo_put(struct cifsFileInfo *cifs_file);
> >
> > #define CIFS_CACHE_READ_FLG 1
> > @@ -1907,6 +1907,7 @@ void cifs_queue_oplock_break(struct cifsFileInfo *cfile);
> > extern const struct slow_work_ops cifs_oplock_break_ops;
> > extern struct workqueue_struct *cifsiod_wq;
> > extern struct workqueue_struct *decrypt_wq;
> > +extern struct workqueue_struct *fileinfo_put_wq;
> > extern struct workqueue_struct *cifsoplockd_wq;
> > extern __u32 cifs_lock_secret;
> >
> > diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> > index 67e7d0ffe385..d1dedb8fb31f 100644
> > --- a/fs/cifs/file.c
> > +++ b/fs/cifs/file.c
> > @@ -375,30 +375,7 @@ cifsFileInfo_get(struct cifsFileInfo *cifs_file)
> > return cifs_file;
> > }
> >
> > -/**
> > - * cifsFileInfo_put - release a reference of file priv data
> > - *
> > - * Always potentially wait for oplock handler. See _cifsFileInfo_put().
> > - */
> > -void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
> > -{
> > - _cifsFileInfo_put(cifs_file, true);
> > -}
> > -
> > -/**
> > - * _cifsFileInfo_put - release a reference of file priv data
> > - *
> > - * This may involve closing the filehandle @cifs_file out on the
> > - * server. Must be called without holding tcon->open_file_lock and
> > - * cifs_file->file_info_lock.
> > - *
> > - * If @wait_for_oplock_handler is true and we are releasing the last
> > - * reference, wait for any running oplock break handler of the file
> > - * and cancel any pending one. If calling this function from the
> > - * oplock break handler, you need to pass false.
> > - *
> > - */
> > -void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
> > +void cifsFileInfo_put_final(struct cifsFileInfo *cifs_file)
> > {
> > struct inode *inode = d_inode(cifs_file->dentry);
> > struct cifs_tcon *tcon = tlink_tcon(cifs_file->tlink);
> > @@ -409,7 +386,6 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
> > struct cifsLockInfo *li, *tmp;
> > struct cifs_fid fid;
> > struct cifs_pending_open open;
> > - bool oplock_break_cancelled;
> >
> > spin_lock(&tcon->open_file_lock);
> > spin_lock(&cifsi->open_file_lock);
> > @@ -449,9 +425,6 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
> > spin_unlock(&cifsi->open_file_lock);
> > spin_unlock(&tcon->open_file_lock);
> >
> > - oplock_break_cancelled = wait_oplock_handler ?
> > - cancel_work_sync(&cifs_file->oplock_break) : false;
> > -
> > if (!tcon->need_reconnect && !cifs_file->invalidHandle) {
> > struct TCP_Server_Info *server = tcon->ses->server;
> > unsigned int xid;
> > @@ -462,9 +435,6 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
> > _free_xid(xid);
> > }
> >
> > - if (oplock_break_cancelled)
> > - cifs_done_oplock_break(cifsi);
> > -
> > cifs_del_pending_open(&open);
> >
> > /*
> > @@ -487,6 +457,61 @@ void _cifsFileInfo_put(struct cifsFileInfo *cifs_file, bool wait_oplock_handler)
> > kfree(cifs_file);
> > }
> >
> > +static void cifsFileInfo_put_work(struct work_struct *work)
> > +{
> > + struct cifsFileInfo *cifs_file = container_of(work,
> > + struct cifsFileInfo, put);
> > +
> > + cifsFileInfo_put_final(cifs_file);
> > +}
> > +
> > +/**
> > + * _cifsFileInfo_put - release a reference of file priv data
> > + *
> > + * This may involve closing the filehandle @cifs_file out on the
> > + * server. Must be called without holding tcon->open_file_lock,
> > + * cinode->open_file_lock and cifs_file->file_info_lock.
> > + *
> > + * If @wait_for_oplock_handler is true and we are releasing the last
> > + * reference, wait for any running oplock break handler of the file
> > + * and cancel any pending one. If calling this function from the
> > + * oplock break handler, you need to pass false.
> > + *
> > + */
> > +void _cifsFileInfo_put(struct cifsFileInfo *cifs_file,
> > + bool wait_oplock_handler, bool offload)
> > +{
> > + struct inode *inode = d_inode(cifs_file->dentry);
> > + struct cifsInodeInfo *cifsi = CIFS_I(inode);
> > +
> > + spin_lock(&cifs_file->file_info_lock);
> > + if (cifs_file->count > 1) {
> > + cifs_file->count--;
> > + spin_unlock(&cifs_file->file_info_lock);
> > + return;
> > + }
> > + spin_unlock(&cifs_file->file_info_lock);
> > +
> > + if (wait_oplock_handler && cancel_work_sync(&cifs_file->oplock_break))
> > + cifs_done_oplock_break(cifsi);
>
> At this point the file info is still in the lists and can be
> referenced by other threads not only including oplock break routine.
> So, we can't cancel oplock break here - it would lead to big timeouts
> to other clients trying to open the file because the server will be
> waiting for an oplock break ack.
>
> Let's do it in cifsFileInfo_put_final() as it was originally in
> cifsFileInfo_put() and we do not need an extra *wait_oplock_handler*
> argument - just cancel it unconditionally. If a caller of this
> function don't want to deadlock on himself (like cifs_oplock_break) it
> will just specify *offload* as True.
>
> > +
> > + if (offload) {
> > + INIT_WORK(&cifs_file->put, cifsFileInfo_put_work);
INIT_WORK should be done when initializing cifsFileInfo structure.
> > + queue_work(fileinfo_put_wq, &cifs_file->put);
As I mentioned in the parallel discussion queue_work here may return
False if the same work has been already queued. It may happen in the
following scenario:
T1 gets reference - 1
T1 is in putting the reference - checked ref > 1
T2 gets reference - 2
T1 queues work
T3 (worker) puts the reference - 1 but still didn't exit and remains
in the queue
T2 is in putting the reference - checked ref >1
T2 queues work and it returns false (!) <--- error
Sorry, it wasn't obvious to me when I was suggesting this yesterday.
One way to fix this is to check queue_work output and "goto" to the
beginning of the function if False. But there is always a probability
that we end up in the same situation and it repeats and repeats again.
I think it should resolve itself at some point in time but it doesn't
look like a good approach.
Another way to fix it is to revert the patch to the state it was at
yesterday - to offload only the remaining part of cifsFileInfo_put()
which will allow us to avoid the race from above. I am personally
leaning towards this way.
Other may comments about eliminating the need of *wait_oplock_handler*
and INIT_WORK stand for yesterday's patch too.
Thoughts?
> > + } else
> > + cifsFileInfo_put_final(cifs_file);
> > +}
> > +
> > +/**
> > + * cifsFileInfo_put - release a reference of file priv data
> > + *
> > + * Always potentially wait for oplock handler. See _cifsFileInfo_put().
> > + */
> > +void cifsFileInfo_put(struct cifsFileInfo *cifs_file)
> > +{
> > + _cifsFileInfo_put(cifs_file, true, true);
> > +}
> > +
> > int cifs_open(struct inode *inode, struct file *file)
> >
> > {
> > @@ -808,7 +833,7 @@ cifs_reopen_file(struct cifsFileInfo *cfile, bool can_flush)
> > int cifs_close(struct inode *inode, struct file *file)
> > {
> > if (file->private_data != NULL) {
> > - cifsFileInfo_put(file->private_data);
> > + _cifsFileInfo_put(file->private_data, true, false);
> > file->private_data = NULL;
> > }
> >
> > @@ -4742,7 +4767,7 @@ void cifs_oplock_break(struct work_struct *work)
> > cinode);
> > cifs_dbg(FYI, "Oplock release rc = %d\n", rc);
> > }
> > - _cifsFileInfo_put(cfile, false /* do not wait for ourself */);
> > + _cifsFileInfo_put(cfile, false /* do not wait for ourself */, true);
>
> As mentioned above, here we only need *offload* as True to not wait
> for ourselves.
>
> > cifs_done_oplock_break(cinode);
> > }
> >
> > --
> > 2.13.6
> >
>
> Other than that, I think we the patch is on the right track. It should
> give us an opportunity to do file handle batching easily.
>
> --
> Best regards,
> Pavel Shilovsky
