lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Thu, 21 Oct 2021 21:29:44 +0200 From: Jan Kara <jack@...e.cz> To: Gabriel Krisman Bertazi <krisman@...labora.com> Cc: Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>, Jan Kara <jack@...e.com>, "Darrick J. Wong" <djwong@...nel.org>, Theodore Tso <tytso@....edu>, Dave Chinner <david@...morbit.com>, David Howells <dhowells@...hat.com>, Khazhismel Kumykov <khazhy@...gle.com>, linux-fsdevel <linux-fsdevel@...r.kernel.org>, Ext4 <linux-ext4@...r.kernel.org>, Linux API <linux-api@...r.kernel.org>, kernel@...labora.com Subject: Re: [PATCH v8 20/32] fanotify: Dynamically resize the FAN_FS_ERROR pool On Thu 21-10-21 15:17:33, Gabriel Krisman Bertazi wrote: > Jan Kara <jack@...e.cz> writes: > > > On Tue 19-10-21 08:50:23, Amir Goldstein wrote: > >> On Tue, Oct 19, 2021 at 3:03 AM Gabriel Krisman Bertazi > >> <krisman@...labora.com> wrote: > >> > > >> > Allow the FAN_FS_ERROR group mempool to grow up to an upper limit > >> > dynamically, instead of starting already at the limit. This doesn't > >> > bother resizing on mark removal, but next time a mark is added, the slot > >> > will be either reused or resized. Also, if several marks are being > >> > removed at once, most likely the group is going away anyway. > >> > > >> > Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com> > >> > --- > >> > fs/notify/fanotify/fanotify_user.c | 26 +++++++++++++++++++++----- > >> > include/linux/fsnotify_backend.h | 1 + > >> > 2 files changed, 22 insertions(+), 5 deletions(-) > >> > > >> > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c > >> > index f77581c5b97f..a860c286e885 100644 > >> > --- a/fs/notify/fanotify/fanotify_user.c > >> > +++ b/fs/notify/fanotify/fanotify_user.c > >> > @@ -959,6 +959,10 @@ static int fanotify_remove_mark(struct fsnotify_group *group, > >> > > >> > removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags, > >> > umask, &destroy_mark); > >> > + > >> > + if (removed & FAN_FS_ERROR) > >> > + group->fanotify_data.error_event_marks--; > >> > + > >> > if (removed & fsnotify_conn_mask(fsn_mark->connector)) > >> > fsnotify_recalc_mask(fsn_mark->connector); > >> > if (destroy_mark) > >> > @@ -1057,12 +1061,24 @@ static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group, > >> > > >> > static int fanotify_group_init_error_pool(struct fsnotify_group *group) > >> > { > >> > - if (mempool_initialized(&group->fanotify_data.error_events_pool)) > >> > - return 0; > >> > + int ret; > >> > + > >> > + if (group->fanotify_data.error_event_marks >= > >> > + FANOTIFY_DEFAULT_MAX_FEE_POOL) > >> > + return -ENOMEM; > >> > > >> > - return mempool_init_kmalloc_pool(&group->fanotify_data.error_events_pool, > >> > - FANOTIFY_DEFAULT_MAX_FEE_POOL, > >> > - sizeof(struct fanotify_error_event)); > >> > + if (!mempool_initialized(&group->fanotify_data.error_events_pool)) > >> > + ret = mempool_init_kmalloc_pool( > >> > + &group->fanotify_data.error_events_pool, > >> > + 1, sizeof(struct fanotify_error_event)); > >> > + else > >> > + ret = mempool_resize(&group->fanotify_data.error_events_pool, > >> > + group->fanotify_data.error_event_marks + 1); > >> > + > >> > + if (!ret) > >> > + group->fanotify_data.error_event_marks++; > >> > + > >> > + return ret; > >> > } > >> > >> This is not what I had in mind. > >> I was thinking start with ~32 and double each time limit is reached. > > > > Do you mean when number of FS_ERROR marks reaches the number of preallocated > > events? We could do that but note that due to mempool implementation limits > > there cannot be more than 255 preallocated events, also mempool_resize() > > will only update number of slots for preallocated events but these slots > > will be empty. You have to manually allocate and free events to fill these > > slots with preallocated events. > > > >> And also, this code grows the pool to infinity with add/remove mark loop. > > > > I see a cap at FANOTIFY_DEFAULT_MAX_FEE_POOL in the code there. But I don't > > think there's a good enough reason to hard-limit number of FS_ERROR marks > > at 128. As I explained in the previous version of the series, in vast > > majority of cases we will not use even a single preallocated event... > > > >> Anyway, since I clearly did not understand how mempool works and > >> Jan had some different ideas I would leave it to Jan to explain > >> how he wants the mempool init limit and resize to be implemented. > > > > Honestly, I'm for keeping it simple for now. Just 32 preallocated events > > and try to come up with something more clever only if someone actually > > complains. > > So, If I understand correctly the conclusion, you are fine if I revert to > the version I had in v7: 32 fields pre-allocated, no dynamic growth and > just limit the number of FAN_FS_ERROR marks to <= 32? Yes to 32 preallocated events, no to FAN_FS_ERROR mark limit - just keep number of marks unlimited. IMO it would be a hard to understand limit for userspace. > In the future, if this ever becomes a problem, we look into dynamic > resizing/increasing the limit? Yes. > I think either option is fine by me. I thought that growing 1 by 1 like > I did here would be ugly, but before sending the patch, I checked and I > was quite satisfied with how simple mempool_resize actually is. Yes, mempool resize is simple, except that you have to care not to resize to more than 255 and also for mempool_resize() to guarantee anything you have to allocate and free events to fill slots at which point things become a bit ugly. Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
Powered by blists - more mailing lists