| Message ID | 20191119131850.5675-1-aryabinin@virtuozzo.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | mm/ksm: Don't WARN if page is still mapped in remove_stable_node() | expand |
On Tue, 19 Nov 2019, Andrey Ryabinin wrote: > It's possible to hit the WARN_ON_ONCE(page_mapped(page)) in > remove_stable_node() when it races with __mmput() and squeezes > in between ksm_exit() and exit_mmap(). > > WARNING: CPU: 0 PID: 3295 at mm/ksm.c:888 remove_stable_node+0x10c/0x150 > > Call Trace: > remove_all_stable_nodes+0x12b/0x330 > run_store+0x4ef/0x7b0 > kernfs_fop_write+0x200/0x420 > vfs_write+0x154/0x450 > ksys_write+0xf9/0x1d0 > do_syscall_64+0x99/0x510 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Remove the warning as there is nothing scary going on. > > Fixes: cbf86cfe04a6 ("ksm: remove old stable nodes more thoroughly") > Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Thanks - Acked-by: Hugh Dickins <hughd@google.com> > Cc: <stable@vger.kernel.org> For removing a WARN_ON_ONCE? No, I don't think this needs to go to stable; but I won't resist if Andrew or autobot insist otherwise. > --- > mm/ksm.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/mm/ksm.c b/mm/ksm.c > index dbee2eb4dd05..7905934cd3ad 100644 > --- a/mm/ksm.c > +++ b/mm/ksm.c > @@ -885,13 +885,13 @@ static int remove_stable_node(struct stable_node *stable_node) > return 0; > } > > - if (WARN_ON_ONCE(page_mapped(page))) { > - /* > - * This should not happen: but if it does, just refuse to let > - * merge_across_nodes be switched - there is no need to panic. > - */ > - err = -EBUSY; > - } else { > + /* > + * Page could be still mapped if this races with __mmput() running in > + * between ksm_exit() and exit_mmap(). Just refuse to let > + * merge_across_nodes/max_page_sharing be switched. Good comment, thank you. > + */ > + err = -EBUSY; > + if (!page_mapped(page)) { > /* > * The stable node did not yet appear stale to get_ksm_page(), > * since that allows for an unmapped ksm page to be recognized > -- > 2.23.0
diff --git a/mm/ksm.c b/mm/ksm.c index dbee2eb4dd05..7905934cd3ad 100644 --- a/mm/ksm.c +++ b/mm/ksm.c @@ -885,13 +885,13 @@ static int remove_stable_node(struct stable_node *stable_node) return 0; } - if (WARN_ON_ONCE(page_mapped(page))) { - /* - * This should not happen: but if it does, just refuse to let - * merge_across_nodes be switched - there is no need to panic. - */ - err = -EBUSY; - } else { + /* + * Page could be still mapped if this races with __mmput() running in + * between ksm_exit() and exit_mmap(). Just refuse to let + * merge_across_nodes/max_page_sharing be switched. + */ + err = -EBUSY; + if (!page_mapped(page)) { /* * The stable node did not yet appear stale to get_ksm_page(), * since that allows for an unmapped ksm page to be recognized
It's possible to hit the WARN_ON_ONCE(page_mapped(page)) in remove_stable_node() when it races with __mmput() and squeezes in between ksm_exit() and exit_mmap(). WARNING: CPU: 0 PID: 3295 at mm/ksm.c:888 remove_stable_node+0x10c/0x150 Call Trace: remove_all_stable_nodes+0x12b/0x330 run_store+0x4ef/0x7b0 kernfs_fop_write+0x200/0x420 vfs_write+0x154/0x450 ksys_write+0xf9/0x1d0 do_syscall_64+0x99/0x510 entry_SYSCALL_64_after_hwframe+0x49/0xbe Remove the warning as there is nothing scary going on. Fixes: cbf86cfe04a6 ("ksm: remove old stable nodes more thoroughly") Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com> Cc: <stable@vger.kernel.org> --- mm/ksm.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-)